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• How do I get an overview and a methodology for programming in Python

  - by Peter Nielsen

  I've started to learn Python and programming from scratch. I have not programmed before so it's a new experience. I do seem to grasp most of the concepts, from variables to definitions and modules. I still need to learn a lot more about what the different libraries and modules do and also I lack knowledge on OOP and classes in Python. I see people who just program in Python like that's all they have ever done and I am still just coming to grips with it. Is there a way, some tools, a logical methodology that would give me an overview or a good hold of how to handle programming problems ? For instance, I'm trying to create a parser which we need at the office . I also need to create a spider that would collect links from various websites. Is there a formidable way of studying the various modules to see what is needed ? Or is it just nose to the grind stone and understand what the documentation says ? Sorry for the lengthy question..

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• A doubt on DOM parser used with Python

  - by fixxxer

  I'm using the following python code to search for a node in an XML file and changing the value of an attribute of one of it's children.Changes are happening correctly when the node is displayed using toxml().But, when it is written to a file, the attributes rearrange themselves(as seen in the Source and the Final XML below). Could anyone explain how and why this happen? Python code: #!/usr/bin/env python import xml from xml.dom.minidom import parse dom=parse("max.xml") #print "Please enter the store name:" for sku in dom.getElementsByTagName("node"): if sku.getAttribute("name") == "store": sku.childNodes[1].childNodes[5].setAttribute("value","Delhi,India") print sku.toxml() xml.dom.ext.PrettyPrint(dom, open("new.xml", "w")) a part of the Source XML: <node name='store' node_id='515' module='mpx.lib.node.simple_value.SimpleValue' config_builder='' inherant='false' description='Configurable Value'> <match> <property name='1' value='point'/> <property name='2' value='0'/> <property name='val' value='Store# 09204 Staten Island, NY'/> <property name='3' value='str'/> </match> </node> Final XML : <node config_builder="" description="Configurable Value" inherant="false" module="mpx.lib.node.simple_value.SimpleValue" name="store" node_id="515"> <match> <property name="1" value="point"/> <property name="2" value="0"/> <property name="val" value="Delhi,India"/> <property name="3" value="str"/> </match> </node>

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• Outgoing UDP sniffer in python?

  - by twneale

  I want to figure out whether my computer is somehow causing a UDP flood that is originating from my network. So that's my underlying problem, and what follows is simply my non-network-person attempt to hypothesize a solution using python. I'm extrapolating from recipe 13.1 ("Passing Messages with Socket Datagrams") from the python cookbook (also here). Would it possible/sensible/not insane to try somehow writing an outgoing UDP proxy in python, so that outgoing packets could be logged before being sent on their merry way? If so, how would one go about it? Based on my quick research, perhaps I could start a server process listening on suspect UDP ports and log anything that gets sent, then forward it on, such as: import socket s =socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.bind(("", MYPORT)) while True: packet = dict(zip('data', 'addr'), s.recvfrom(1,024)) log.info("Recieved {data} from {addr}.".format(**packet)) But what about doing this for a large number of ports simultaneously? Impractical? Are there drawbacks or other reasons not to bother with this? Is there a better way to solve this problem (please be gentle).

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• python thread prob after build

  - by Apache

  hi expert, i'm having task to scan wifi at specific interval and send it to the server, i've it in python and its works fine when i run manually, then build it to package and when run there is no progress at all, i already ask this question before at http://stackoverflow.com/questions/2735410/python-scritp-problem-once-build-and-package-it, then, i re-modify my code as below, then i found that thread is not functioning once i build, #!/usr/bin/env python import subprocess,threading,... configFile = open('/opt/Jemapoh_Wifi/config.txt', 'r') url = configFile.readline().strip() intervalTime = configFile.readline().strip() status = configFile.readline().strip() print "url "+url print "intervalTime "+intervalTime print "Status "+status.strip() def getMacAddress(): proc = subprocess.Popen('ifconfig -a wlan0 | grep HWaddr | sed \'/^.*HWaddr */!d; s///;q\'', shell=True, stdout=subprocess.PIPE, ) macAddress = proc.communicate()[0].strip() return macAddress def getTimestamp(): from time import strftime timeStamp = strftime("%Y-%m-%d %H:%M:%S") return timeStamp def scanWifi(): try: print "Scanning..." proc = subprocess.Popen('iwlist scan 2>/dev/null', shell=True, stdout=subprocess.PIPE, ) stdout_str = proc.communicate()[0] stdout_list=stdout_str.split('\n') essid=[] rssi=[] preQuality=[] for line in stdout_list: line=line.strip() match=re.search('ESSID:"(\S+)"',line) if match: essid.append(match.group(1)) match=re.search('Quality=(\S+)',line) if match: preQuality.append(match.group(1)) for qualityConversion in preQuality: qualityConversion = qualityConversion.split()[0].split('/') temp = str(int(round(float(qualityConversion[0]) / float(qualityConversion[1]) * 100))).rjust(2) rssi.append(temp) dataToPost = '{"userId":"' + getMacAddress() + '","timestamp":"' + getTimestamp() + '","wifi":[' for no in range(len(essid)): dataToPost += '{"ssid":"' + essid[no] + '","rssi":"' + rssi[no] + '"}' if no+1 == len(essid): pass else: dataToPost += ',' dataToPost += ']}' query_args = {"data":dataToPost} request = urllib2.Request(url) request.add_data(urllib.urlencode(query_args)) request.add_header('Content-Type', 'application/x-www-form-urlencoded') print "Waiting for server response..." print urllib2.urlopen(request).read() print "Data Sent @ " + getTimestamp() print "------------------------------------------------------" t = threading.Timer(int(intervalTime), scanWifi).start() except Exception, e: print e t = threading.Timer(int(intervalTime), scanWifi) t.start() once build, its not reaching the thread, do can anyone help, why the thread is not working after build thanks

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• Python - Open default mail client using mailto, with multiple recipients

  - by victorhooi

  Hi, I'm attempting to write a Python function to send an email to a list of users, using the default installed mail client. I want to open the email client, and give the user the opportunity to edit the list of users or the email body. I did some searching, and according to here: http://www.sightspecific.com/~mosh/WWW_FAQ/multrec.html It's apparently against the RFC spec to put multiple comma-delimited recipients in a mailto link. However, that's the way everybody else seems to be doing it. What exactly is the modern stance on this? Anyhow, I found the following two sites: http://2ality.blogspot.com/2009/02/generate-emails-with-mailto-urls-and.html http://www.megasolutions.net/python/invoke-users-standard-mail-client-64348.aspx which seem to suggest solutions using urllib.parse (url.parse.quote for me), and webbrowser.open. I tried the sample code from the first link (2ality.blogspot.com), and that worked fine, and opened my default mail client. However, when I try to use the code in my own module, it seems to open up my default browser, for some weird reason. No funny text in the address bar, it just opens up the browser. The email_incorrect_phone_numbers() function is in the Employees class, which contains a dictionary (employee_dict) of Employee objects, which themselves have a number of employee attributes (sn, givenName, mail etc.). Full code is actually here (http://stackoverflow.com/questions/2963975/python-converting-csv-to-objects-code-design) from urllib.parse import quote import webbrowser .... def email_incorrect_phone_numbers(self): email_list = [] for employee in self.employee_dict.values(): if not PhoneNumberFormats.standard_format.search(employee.telephoneNumber): print(employee.telephoneNumber, employee.sn, employee.givenName, employee.mail) email_list.append(employee.mail) recipients = ', '.join(email_list) webbrowser.open("mailto:%s?subject=%s&body=%s" % (recipients, quote("testing"), quote('testing')) ) Any suggestions? Cheers, Victor

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• Efficient method to calculate the rank vector of a list in Python

  - by Tamás

  I'm looking for an efficient way to calculate the rank vector of a list in Python, similar to R's rank function. In a simple list with no ties between the elements, element i of the rank vector of a list l should be x if and only if l[i] is the x-th element in the sorted list. This is simple so far, the following code snippet does the trick: def rank_simple(vector): return [rank for rank in sorted(range(n), key=vector.__getitem__)] Things get complicated, however, if the original list has ties (i.e. multiple elements with the same value). In that case, all the elements having the same value should have the same rank, which is the average of their ranks obtained using the naive method above. So, for instance, if I have [1, 2, 3, 3, 3, 4, 5], the naive ranking gives me [0, 1, 2, 3, 4, 5, 6], but what I would like to have is [0, 1, 3, 3, 3, 5, 6]. Which one would be the most efficient way to do this in Python? Footnote: I don't know if NumPy already has a method to achieve this or not; if it does, please let me know, but I would be interested in a pure Python solution anyway as I'm developing a tool which should work without NumPy as well.

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• A question about DOM parser used with Python

  - by fixxxer

  I'm using the following python code to search for a node in an XML file and changing the value of an attribute of one of it's children.Changes are happening correctly when the node is displayed using toxml().But, when it is written to a file, the attributes rearrange themselves(as seen in the Source and the Final XML below). Could anyone explain how and why this happen? Python code: #!/usr/bin/env python import xml from xml.dom.minidom import parse dom=parse("max.xml") #print "Please enter the store name:" for sku in dom.getElementsByTagName("node"): if sku.getAttribute("name") == "store": sku.childNodes[1].childNodes[5].setAttribute("value","Delhi,India") print sku.toxml() xml.dom.ext.PrettyPrint(dom, open("new.xml", "w")) a part of the Source XML: <node name='store' node_id='515' module='mpx.lib.node.simple_value.SimpleValue' config_builder='' inherant='false' description='Configurable Value'> <match> <property name='1' value='point'/> <property name='2' value='0'/> <property name='val' value='Store# 09204 Staten Island, NY'/> <property name='3' value='str'/> </match> </node> Final XML : <node config_builder="" description="Configurable Value" inherant="false" module="mpx.lib.node.simple_value.SimpleValue" name="store" node_id="515"> <match> <property name="1" value="point"/> <property name="2" value="0"/> <property name="val" value="Delhi,India"/> <property name="3" value="str"/> </match> </node>

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• python-iptables: Cryptic error when allowing incoming TCP traffic on port 1234

  - by Lucas Kauffman

  I wanted to write an iptables script in Python. Rather than calling iptables itself I wanted to use the python-iptables package. However I'm having a hard time getting some basic rules setup. I wanted to use the filter chain to accept incoming TCP traffic on port 1234. So I wrote this: import iptc chain = iptc.Chain(iptc.TABLE_FILTER,"INPUT") rule = iptc.Rule() target = iptc.Target(rule,"ACCEPT") match = iptc.Match(rule,'tcp') match.dport='1234' rule.add_match(match) rule.target = target chain.insert_rule(rule) However when I run this I get this thrown back at me: Traceback (most recent call last): File "testing.py", line 9, in <module> chain.insert_rule(rule) File "/usr/local/lib/python2.6/dist-packages/iptc/__init__.py", line 1133, in insert_rule self.table.insert_entry(self.name, rbuf, position) File "/usr/local/lib/python2.6/dist-packages/iptc/__init__.py", line 1166, in new obj.refresh() File "/usr/local/lib/python2.6/dist-packages/iptc/__init__.py", line 1230, in refresh self._free() File "/usr/local/lib/python2.6/dist-packages/iptc/__init__.py", line 1224, in _free self.commit() File "/usr/local/lib/python2.6/dist-packages/iptc/__init__.py", line 1219, in commit raise IPTCError("can't commit: %s" % (self.strerror())) iptc.IPTCError: can't commit: Invalid argument Exception AttributeError: "'NoneType' object has no attribute 'get_errno'" in <bound method Table.__del__ of <iptc.Table object at 0x7fcad56cc550>> ignored Does anyone have experience with python-iptables that could enlighten on what I did wrong?

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• Slow Python HTTP server on localhost

  - by Abiel

  I am experiencing some performance problems when creating a very simple Python HTTP server. The key issue is that performance is varying depending on which client I use to access it, where the server and all clients are being run on the local machine. For instance, a GET request issued from a Python script (urllib2.urlopen('http://localhost/').read()) takes just over a second to complete, which seems slow considering that the server is under no load. Running the GET request from Excel using MSXML2.ServerXMLHTTP also feels slow. However, requesting the data Google Chrome or from RCurl, the curl add-in for R, yields an essentially instantaneous response, which is what I would expect. Adding further to my confusion is that I do not experience any performance problems for any client when I am on my computer at work (the performance problems are on my home computer). Both systems run Python 2.6, although the work computer runs Windows XP instead of 7. Below is my very simple server example, which simply returns 'Hello world' for any get request. from BaseHTTPServer import BaseHTTPRequestHandler, HTTPServer class MyHandler(BaseHTTPRequestHandler): def do_GET(self): print("Just received a GET request") self.send_response(200) self.send_header("Content-type", "text/html") self.end_headers() self.wfile.write('Hello world') return def log_request(self, code=None, size=None): print('Request') def log_message(self, format, *args): print('Message') if __name__ == "__main__": try: server = HTTPServer(('localhost', 80), MyHandler) print('Started http server') server.serve_forever() except KeyboardInterrupt: print('^C received, shutting down server') server.socket.close() Note that in MyHandler I override the log_request() and log_message() functions. The reason is that I read that a fully-qualified domain name lookup performed by one of these functions might be a reason for a slow server. Unfortunately setting them to just print a static message did not solve my problem. Also, notice that I have put in a print() statement as the first line of the do_GET() routine in MyHandler. The slowness occurs prior to this message being printed, meaning that none of the stuff that comes after it is causing a delay.

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• Emailing an excel sheet with SSL in Python

  - by jakecar

  Hi...this is my first post so let me know if there are any common courtesies I should know about. I just started programming 8 months ago, so I am fairly new. I have been doing some projects to get better. A project I'm working on now creates an Excel sheet from inputted data. It's in Python, which I just started learning a couple of weeks ago. I'm attempting to embed part of this Excel sheet into an email, sent from my school address. I have spent hours looking this up, and to no avail. There are two problems I am asking for help with: 1) I have figured out how to send an email from my GMail account, but not from my school address. My school email uses SSL port 465, which I have tried to use, but to no avail. Unfortunately, I have been having a problem setting up outgoing email for this account on my iPhone as well. It may be related? Does anyone know of common issues relating to outgoing email with SSL and Python? 2) Excel has an option of saving a sheet as a HTML. When doing so, I copy and pasted the HTML source and emailed it as an attachment. Unfortunately, the colored text did not transfer over. Does anyone know of a better way of using Python to send an excel sheet embedded in an email? Thanks for your help!

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• UTF-8 HTML and CSS files with BOM (and how to remove the BOM with Python)

  - by Cameron

  First, some background: I'm developing a web application using Python. All of my (text) files are currently stored in UTF-8 with the BOM. This includes all my HTML templates and CSS files. These resources are stored as binary data (BOM and all) in my DB. When I retrieve the templates from the DB, I decode them using template.decode('utf-8'). When the HTML arrives in the browser, the BOM is present at the beginning of the HTTP response body. This generates a very interesting error in Chrome: Extra <html> encountered. Migrating attributes back to the original <html> element and ignoring the tag. Chrome seems to generate an <html> tag automatically when it sees the BOM and mistakes it for content, making the real <html> tag an error. So, using Python, what is the best way to remove the BOM from my UTF-8 encoded templates (if it exists -- I can't guarantee this in the future)? For other text-based files like CSS, will major browsers correctly interpret (or ignore) the BOM? They are being sent as plain binary data without .decode('utf-8'). Note: I am using Python 2.5. Thanks!

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• Multiple Inheritence with same Base Classes in Python

  - by Jordan Reiter

  I'm trying to wrap my head around multiple inheritance in python. Suppose I have the following base class: class Structure(object): def build(self, *args): print "I am building a structure!" self.components = args And let's say I have two classes that inherit from it: class House(Structure): def build(self, *args): print "I am building a house!" super(House, self).build(*args) class School(Structure): def build(self, type="Elementary", *args): print "I am building a school!" super(School, self).build(*args) Finally, a create a class that uses multiple inheritance: class SchoolHouse(School, House): def build(self, *args): print "I am building a schoolhouse!" super(School, self).build(*args) Then, I create a SchoolHouse object and run build on it: >>> sh = SchoolHouse() >>> sh.build("roof", "walls") I am building a schoolhouse! I am building a house! I am building a structure! So I'm wondering -- what happened to the School class? Is there any way to get Python to run both somehow? I'm wondering specifically because there are a fair number of Django packages out there that provide custom Managers for models. But there doesn't appear to be a way to combine them without writing one or the other of the Managers as inheriting from the other one. It'd be nice to just import both and use both somehow, but looks like it can't be done? Also I guess it'd just help to be pointed to a good primer on multiple inheritance in Python. I have done some work with Mixins before and really enjoy using them. I guess I just wonder if there is any elegant way to combine functionality from two different classes when they inherit from the same base class.

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• Converting Python Script to Vb.NET - Involves Post and Input XML String

  - by Jason Shoulders

  I'm trying to convert a Python Script to Vb.Net. The Python Script appears to accept some XML input data and then takes it to a web URL and does a "POST". I tried some VB.NET code to do it, but I think my approach is off because I got an error back "BadXmlDataErr" plus I can't really format my input XML very well - I'm only doing string and value. The input XML is richer than that. Here is an example of what the XML input data looks like in the Python script: <obj is="MyOrg:realCommand_v1/" > <int name="priority" val="1" /> <real name="value" val="9.5" /> <str name="user" val="MyUserName" /> <reltime name="overrideTime" val="PT60S"/> </obj> Here's the Vb.net code I attempted to convert that: Dim reqparm As New Specialized.NameValueCollection reqparm.Add("priority", "1") reqparm.Add("value", "9.5") reqparm.Add("user", "MyUserName") reqparm.Add("overrideTime", "PT60S") Using client As New Net.WebClient Dim sTheUrl As String = "[My URL]" Dim responsebytes = client.UploadValues(sTheUrl, "POST", MyReqparm) Dim responsebody = (New System.Text.UTF8Encoding).GetString(responsebytes) End Using I feel like I should be doing something else. Can anyone point me to the right direction?

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• Create static instances of a class inside said class in Python

  - by Samir Talwar

  Apologies if I've got the terminology wrong here—I can't think what this particular idiom would be called. I've been trying to create a Python 3 class that statically declares instances of itself inside itself—sort of like an enum would work. Here's a simplified version of the code I wrote: class Test: A = Test("A") B = Test("B") def __init__(self, value): self.value = value def __str__(self): return "Test: " + self.value print(str(Test.A)) print(str(Test.B)) Writing this, I got an exception on line 2 (A = Test("A")). I assume line 3 would also error if it had made it that far. Using __class__ instead of Test gives the same error. File "<stdin>", line 1, in <module> File "<stdin>", line 2, in Test NameError: name 'Test' is not defined Is there any way to refer to the current class in a static context in Python? I could declare these particular variables outside the class or in a separate class, but for clarity's sake, I'd rather not if I can help it. To better demonstrate what I'm trying to do, here's the same example in Java: public class Test { private static final Test A = new Test("A"); private static final Test B = new Test("B"); private final String value; public Test(String value) { this.value = value; } public String toString() { return "Test: " + value; } public static void main(String[] args) { System.out.println(A); System.out.println(B); } } This works as you would expect: it prints: Test: A Test: B How can I do the same thing in Python?

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• Prolog singleton variables in Python

  - by Rubens

  I'm working on a little set of scripts in python, and I came to this: line = "a b c d e f g" a, b, c, d, e, f, g = line.split() I'm quite aware of the fact that these are decisions taken during implementation, but shouldn't (or does) python offer something like: _, _, var_needed, _, _, another_var_needed, _ = line.split() as well as Prolog does offer, in order to exclude the famous singleton variables. I'm not sure, but wouldn't it avoid unnecessary allocation? Or creating references to the result of the split call does not count up as overhead? EDIT: Sorry, my point here is: in Prolog, as far as I'm concerned, in an expression like: test(L, N) :- test(L, 0, N). test([], N, N). test([_|T], M, N) :- V is M + 1, test(T, V, N). The variable represented by _ is not accessible, for what I suppose the reference to the value that does exist in the list [_|T] is not even created. But, in Python, if I use _, I can use the last value assigned to _, and also, I do suppose the assignment occurs for each of the variables _ -- which may be considered an overhead. My question here is if shouldn't there be (or if there is) a syntax to avoid such unnecessary attributions.

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• Square Brackets in Python Regular Expressions (re.sub)

  - by user1479984

  I'm migrating wiki pages from the FlexWiki engine to the FOSwiki engine using Python regular expressions to handle the differences between the two engines' markup languages. The FlexWiki markup and the FOSwiki markup, for reference. Most of the conversion works very well, except when I try to convert the renamed links. Both wikis support renamed links in their markup. For example, Flexwiki uses: "Link To Wikipedia":[http://www.wikipedia.org/] FOSwiki uses: [[http://www.wikipedia.org/][Link To Wikipedia]] both of which produce something that looks like I'm using the regular expression renameLink = re.compile ("\"(?P<linkName>[^\"]+)\":\[(?P<linkTarget>[^\[\]]+)\]") to parse out the link elements from the FlexWiki markup, which after running through something like "Link Name":[LinkTarget] is reliably producing groups <linkName> = Link Name <linkTarget = LinkTarget My issue occurs when I try to use re.sub to insert the parsed content into the FOSwiki markup. My experience with regular expressions isn't anything to write home about, but I'm under the impression that, given the groups <linkName> = Link Name <linkTarget = LinkTarget a line like line = renameLink.sub ( "[[\g<linkTarget>][\g<linkName>]]" , line ) should produce [[LinkTarget][Link Name]] However, in the output to the text files I'm getting [[LinkTarget [[Link Name]] which breaks the renamed links. After a little bit of fiddling I managed a workaround, where line = renameLink.sub ( "[[\g<linkTarget>][ [\g<linkName>]]" , line ) produces [[LinkTarget][ [[Link Name]] which, when displayed in FOSwiki looks like <[[Link Name> <--- Which WORKS, but isn't very pretty. I've also tried line = renameLink.sub ( "[[\g<linkTarget>]" + "[\g<linkName>]]" , line ) which is producing [[linkTarget [[linkName]] There are probably thousands of instances of these renamed links in the pages I'm trying to convert, so fixing it by hand isn't any good. For the record I've run the script under Python 2.5.4 and Python 2.7.3, and gotten the same results. Am I missing something really obvious with the syntax? Or is there an easy workaround?

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• Python vs all the major professional languages [closed]

  - by Matt

  I've been reading up a lot lately on comparisons between Python and a bunch of the more traditional professional languages - C, C++, Java, etc, mainly trying to find out if its as good as those would be for my own purposes. I can't get this thought out of my head that it isn't good for 'real' programming tasks beyond automation and macros. Anyway, the general idea I got from about two hundred forum threads and blog posts is that for general, non-professional-level progs, scripts, and apps, and as long as it's a single programmer (you) writing it, a given program can be written quicker and more efficiently with Python than it could be with pretty much any other language. But once its big enough to require multiple programmers or more complex than a regular person (read: non-professional) would have any business making, it pretty much becomes instantly inferior to a million other languages. Is this idea more or less accurate? (I'm learning Python for my first language and want to be able to make any small app that I want, but I plan on learning C eventually too, because I want to get into driver writing eventually. So I've been trying to research each ones strengths and weaknesses as much as I can.) Anyway, thanks for any input

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• Python to Java translation

  - by obelix1337

  Hello, i get quite short code of algorithm in python, but i need to translate it to Java. I didnt find any program to do that, so i will really appreciate to help translating it. I learned python a very little to know the idea how algorithm work. The biggest problem is because in python all is object and some things are made really very confuzing like sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source)) and "self.adj" is like hashmap with multiple values which i have no idea how to put all together. Is any better collection for this code in java? code is: [CODE] class FlowNetwork(object): def __init__(self): self.adj, self.flow, = {},{} def add_vertex(self, vertex): self.adj[vertex] = [] def get_edges(self, v): return self.adj[v] def add_edge(self, u,v,w=0): self.adj[u].append((v,w)) self.adj[v].append((u,0)) self.flow[(u,v)] = self.flow[(v,u)] = 0 def find_path(self, source, sink, path): if source == sink: return path for vertex, capacity in self.get_edges(source): residual = capacity - self.flow[(source,vertex)] edge = (source,vertex,residual) if residual > 0 and not edge in path: result = self.find_path(vertex, sink, path + [edge]) if result != None: return result def max_flow(self, source, sink): path = self.find_path(source, sink, []) while path != None: flow = min(r for u,v,r in path) for u,v,_ in path: self.flow[(u,v)] += flow self.flow[(v,u)] -= flow path = self.find_path(source, sink, []) return sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source)) g = FlowNetwork() map(g.add_vertex, ['s','o','p','q','r','t']) g.add_edge('s','o',3) g.add_edge('s','p',3) g.add_edge('o','p',2) g.add_edge('o','q',3) g.add_edge('p','r',2) g.add_edge('r','t',3) g.add_edge('q','r',4) g.add_edge('q','t',2) print g.max_flow('s','t') [/CODE] result of this example is "5". algorithm find max flow in graph(linked list or whatever) from source vertex "s" to destination "t". Many thanx for any idea

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• Generating a python file

  - by fema

  Hi! I'm havin issues with python (imo python itself is an issue). I have a txt file, it contains a custom language and I have to translate it to a working python code. The input: import sys n = int(sys.argv[1]) ;;print "Beginning of the program!" LOOP i in range(1,n) {print "The number:";;print i} BRANCH n < 5 {print n ;;print "less than 5"} The wanted output looks exactly like this: import sys n = int(sys.argv[1]) print "Beginning of the program!" for i in range(1,n) : print "The number:" print i if n < 5 : print n print "less than 5" The name of the input file is read from parameter. The out file is out.py. In case of a wrong parameter, it gives an error message. The ;; means a new line. When I tried to do it, I made an array, I read all the lines into it, split by " ". Then I wanted to strip it from the marks I don't need. I made 2 loops, one for the lines, one for the words. So then I started to replace the things. Everything went fine until it came to the } mark. It finds it, but it can not replace or strip it. I have no more idea what to do. Could someone help me, please? Thanks in advance!

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• Python 2.6 does not like appending to existing archives in zip files

  - by user313661

  Hello, In some Python unit tests of a program I'm working on we use in-memory zipfiles for end to end tests. In SetUp() we create a simple zip file, but in some tests we want to overwrite some archives. For this we do "zip.writestr(archive_name, zip.read(archive_name) + new_content)". Something like import zipfile from StringIO import StringIO def Foo(): zfile = StringIO() zip = zipfile.ZipFile(zfile, 'a') zip.writestr( "foo", "foo content") zip.writestr( "bar", "bar content") zip.writestr( "foo", zip.read("foo") + "some more foo content") print zip.read("bar") Foo() The problem is that this works fine in Python 2.4 and 2.5, but not 2.6. In Python 2.6 this fails on the print line with "BadZipfile: File name in directory "bar" and header "foo" differ." It seems that it is reading the correct file bar, but that it thinks it should be reading foo instead. I'm at a loss. What am I doing wrong? Is this not supported? I tried searching the web but could find no mention of similar problems. I read the zipfile documentation, but could not find anything (that I thought was) relevant, especially since I'm calling read() with the filename string. Any ideas? Thank you in advance!

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• Porting Python algorithm to C++ - different solution

  - by cb0

  Hello, I have written a little brute string generation script in python to generate all possible combinations of an alphabet within a given length. It works quite nice, but for the reason I wan't it to be faster I try to port it to C++. The problem is that my C++ Code is creating far too much combination for one word. Heres my example in python: ./test.py gives me aaa aab aac aad aa aba .... while ./test (the c++ programm gives me) aaa aaa aaa aaa aa Here I also get all possible combinations, but I get them twice ore more often. Here is the Code for both programms: #!/usr/bin/env python import sys #Brute String Generator #Start it with ./brutestringer.py 4 6 "abcdefghijklmnopqrstuvwxyz1234567890" "" #will produce all strings with length 4 to 6 and chars from a to z and numbers 0 to 9 def rec(w, p, baseString): for c in "abcd": if (p<w - 1): rec(w, p + 1, baseString + "%c" % c) print baseString for b in range(3,4): rec(b, 0, "") And here the C++ Code #include <iostream> using namespace std; string chars="abcd"; void rec(int w,int b,string p){ unsigned int i; for(i=0;i<chars.size();i++){ if(b < (w-1)){ rec(w, (b+1), p+chars[i]); } cout << p << "\n"; } } int main () { int a=3, b=0; rec (a+1,b, ""); return 0; } Does anybody see my fault ? I don't have much experience with C++. Thanks indeed

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• python interactive mode module import issue

  - by Jeff

  I believe I have what would be called a scope issue, perhaps name space. Not too sure I'm new to python. I'm trying to make a module that will search through a list using regular expressions. I'm sure there is a better way of doing it but this error that I'm getting is bugging me and I want to understand why. here's my code: class relist(list): def __init__(self, l): list.__init__(self, l) def __getitem__(self, rexp): r = re.compile(rexp) res = filter(r.match, self) return res if __name__ == '__main__': import re listl = [x+y for x in 'test string' for y in 'another string for testing'] print(listl) test = relist(listl) print('----------------------------------') print(test['[s.]']) When I run this code through the command line it works the way I expect it to; however when I run it through python interactive mode I get the error >>> test['[s.]'] Traceback (most recent call last): File "<stdin>", line 1, in <module> File "relist.py", line 8, in __getitem__ r = re.compile(rexp) NameError: global name 're' is not defined While in the interactive mode I do import re and I am able to use the re functions, but for some reason when I'm trying to execute the module it doesn't work. Do I need to import re into the scope of the class? I wouldn't think so because doesn't python search through other scopes if it's not found in the current one? I appreciate your help, and if there is a better way of doing this search I would be interested in knowing. Thanks

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• Communicating with a running python daemon

  - by hanksims

  I wrote a small Python application that runs as a daemon. It utilizes threading and queues. I'm looking for general approaches to altering this application so that I can communicate with it while it's running. Mostly I'd like to be able to monitor its health. In a nutshell, I'd like to be able to do something like this: python application.py start # launches the daemon Later, I'd like to be able to come along and do something like: python application.py check_queue_size # return info from the daemonized process To be clear, I don't have any problem implementing the Django-inspired syntax. What I don't have any idea how to do is to send signals to the daemonized process (start), or how to write the daemon to handle and respond to such signals. Like I said above, I'm looking for general approaches. The only one I can see right now is telling the daemon constantly log everything that might be needed to a file, but I hope there's a less messy way to go about it. UPDATE: Wow, a lot of great answers. Thanks so much. I think I'll look at both Pyro and the web.py/Werkzeug approaches, since Twisted is a little more than I want to bite off at this point. The next conceptual challenge, I suppose, is how to go about talking to my worker threads without hanging them up. Thanks again.

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• Efficient way to get highly correlated pairs from large data set in Python or R

  - by Akavall

  I have a large data set (Let's say 10,000 variables with about 1000 elements each), we can think of it as 2D list, something like: [[variable_1], [variable_2], ............ [variable_n] ] I want to extract highly correlated variable pairs from that data. I want "highly correlated" to be a parameter that I can choose. I don't need all pairs to be extracted, and I don't necessarily want the most correlated pairs. As long as there is an efficient method that gets me highly correlated pairs I am happy. Also, it would be nice if a variable does not show up in more than one pair. Although this might not be crucial. Of course, there is a brute force way to finding such pairs, but it is too slow for me. I've googled around for a bit and found some theoretical work on this issue, but I wasn't able for find a package that could do what I am looking for. I mostly work in python, so a package in python would be most helpful, but if there exists a package in R that does what I am looking for it will be great. Does anyone know of a package that does the above in Python or R? Or any other ideas? Thank You in Advance

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• Python to C/C++ const char question

  - by tsukemonoki

  I am extending Python with some C++ code. One of the functions I'm using has the following signature: int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict, char *format, char **kwlist, ...); (link: http://docs.python.org/release/1.5.2p2/ext/parseTupleAndKeywords.html) The parameter of interest is kwlist. In the link above, examples on how to use this function are given. In the examples, kwlist looks like: static char *kwlist[] = {"voltage", "state", "action", "type", NULL}; When I compile this using g++, I get the warning: warning: deprecated conversion from string constant to ‘char*’ So, I can change the static char* to a static const char*. Unfortunately, I can't change the Python code. So with this change, I get a different compilation error (can't convert char** to const char**). Based on what I've read here, I can turn on compiler flags to ignore the warning or I can cast each of the constant strings in the definition of kwlist to char *. Currently, I'm doing the latter. What are other solutions? Sorry if this question has been asked before. I'm new.

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