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  • Python lambda returning None instead of empty string

    - by yoshi
    I have the following lambda function: f = lambda x: x == None and '' or x It should return an empty string if it receives None as the argument, or the argument if it's not None. For example: >>> f(4) 4 >>> f(None) >>> If I call f(None) instead of getting an empty string I get None. I printed the type of what the function returned and I got NoneType. I was expecting string. type('') returns string, so I'd like to know why the lambda doesn't return an empty string when I pass None as an argument. I'm fairly new to lambdas so I might have misunderstood some things about how they work.

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  • Windows path in python

    - by Gareth
    Hi all. What is the best way to represent a windows directory, for example "C:\meshes\as"? I have been trying to modify a script but it never works because I can't seem to get the directory right, I assume because of the '\' acting as escape character? Thanks, Gareth

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  • Proper way to assert type of variable in Python

    - by Morlock
    In using a function, I wish to ensure that the type of the variables are as expected. How to do it right? Here is an example fake function trying to do just this before going on with its role: def my_print(text, begin, end): """Print text in UPPER between 'begin' and 'end' in lower """ for i in (text, begin, end): assert type(i) == type("") out = begin.lower() + text.upper() + end.lower() print out Is this approach valid? Should I use something else than type(i) == type("") ? Should I use try/except instead? Thanks pythoneers

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  • Python - Strange Behavior in re.sub

    - by Greg
    Here's the code I'm running: import re FIND_TERM = r'C:\\Program Files\\Microsoft SQL Server\\90\\DTS\\Binn\\DTExec\.exe' rfind_term = re.compile(FIND_TERM,re.I) REPLACE_TERM = 'C:\\Program Files\\Microsoft SQL Server\\100\\DTS\\Binn\\DTExec.exe' test = r'something C:\Program Files\Microsoft SQL Server\90\DTS\Binn\DTExec.exe something' print rfind_term.sub(REPLACE_TERM,test) And the result I get is: something C:\Program Files\Microsoft SQL Server@\DTS\Binn\DTExec.exe something Why is there an @ sign?

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  • Fast iterating over first n items of an iterable (not a list) in python

    - by martinthenext
    Hello! I'm looking for a pythonic way of iterating over first n items of an iterable (upd: not a list in a common case, as for lists things are trivial), and it's quite important to do this as fast as possible. This is how I do it now: count = 0 for item in iterable: do_something(item) count += 1 if count >= n: break Doesn't seem neat to me. Another way of doing this is: for item in itertools.islice(iterable, n): do_something(item) This looks good, the question is it fast enough to use with some generator(s)? For example: pair_generator = lambda iterable: itertools.izip(*[iter(iterable)]*2) for item in itertools.islice(pair_generator(iterable), n): so_something(item) Will it run fast enough as compared to the first method? Is there some easier way to do it?

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  • what's faster: merging lists or dicts in python?

    - by tipu
    I'm working with an app that is cpu-bound more than memory bound, and I'm trying to merge two things whether they be sets or dicts. Now the thing is i can choose either one, but I'm wondering if merging dicts would be faster since it's all in memory? Or is it always going to be O(n), n being the size of the smaller set. The reason I asked about dicts rather than sets is because I can't convert a set to json, because that results in {key1, key2, key3} and json needs a key/value pair, so I am using a dict so json dumps returns {key1:1, key2:1, key3:1}. Yes this is wasteful, but if it proves to be faster then I'm okay with it.

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  • Using Python's ConfigParser to read a file without section name

    - by Arrieta
    Hello: I am using ConfigParser to read the runtime configuration of a script. I would like to have the flexibility of not providing a section name (there are scripts which are simple enough; they don't need a 'section'). ConfigParser will throw the NoSectionError exception, and will not accept the file. How can I make ConfigParser simply retrieve the (key, value) tuples of a config file without section names? For instance: key1=val1 key2:val2 I would rather not write to the config file.

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  • python, wrapping class returning the average of the wrapped members

    - by João Portela
    The title isn't very clear but I'll try to explain. Having this class: class Wrapped(object): def method_a(self): # do some operations return n def method_b(self): # also do some operations return n I wan't to have a class that performs the same way as this one: class Wrapper(object): def __init__(self): self.ws = [Wrapped(1),Wrapped(2),Wrapped(3)] def method_a(self): results=[Wrapped.method_a(w) for w in self.ws] sum_ = sum(results,0.0) average = sum_/len(self.ws) return average def method_b(self): results=[Wrapped.method_b(w) for w in self.ws] sum_ = sum(results,0.0) average = sum_/len(self.ws) return average obviously this is not the actual problem at hand (it is not only two methods), and this code is also incomplete (only included the minimum to explain the problem). So, what i am looking for is a way to obtain this behavior. Meaning, whichever method is called in the wrapper class, call that method for all the Wrapped class objects and return the average of their results. Can it be done? how? Thanks in advance. ps-didn't know which tags to include...

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  • Flickr API automated login using Python library flickrapi

    - by Dave Aaron Smith
    I have a web application that I want to sync with Flickr. I don't want the users to have to log into Flickr so I plan to use a single login. I believe I'll need to do something like this: import flickrapi flickr = flickrapi.FlickrAPI(myKey, mySecret) (token, frob) = flickr.get_token_part_one(perms='write', my_auth_callback) flickr.get_token_part_two((token, frob,)) flickr.what_have_you(... I don't know what my_auth_callback should look like though. I suspect it will have to post my login information to flickr. Could I do the get_token_part_one step just once manually perhaps and then re-use it in get_token_part_two?

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  • Reading HTTP server push streams with Python

    - by Sam
    I'm playing around trying to write a client for a site which provides data as an HTTP stream (aka HTTP server push). However, urllib2.urlopen() grabs the stream in its current state and then closes the connection. I tried skipping urllib2 and using httplib directly, but this seems to have the same behaviour. Is there a way to get the stream to stay open, so it can be checked each program loop for new contents, rather than waiting for the whole thing to be redownloaded every few seconds, introducing lag?

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  • Calling/selecting variables (float valued) with user input in Python

    - by Jonathan Straus
    I've been working on a computational physics project (plotting related rates of chemical reactants with respect to eachother to show oscillatory behavior) with a fair amount of success. However, one of my simulations involves more than two active oscillating agents (five, in fact) which would obviously be unsuitable for any single visual plot... My scheme was hence to have the user select which two reactants they wanted plotted on the x-axis and y-axis respectively. I tried (foolishly) to convert string input values into the respective variable names, but I guess I need a radically different approach if any exist? If it helps clarify any, here is part of my code: def coupledBrusselator(A, B, t_trial,display_x,display_y): t = 0 t_step = .01 X = 0 Y = 0 E = 0 U = 0 V = 0 dX = (A) - (B+1)*(X) + (X**2)*(Y) dY = (B)*(X) - (X**2)*(Y) dE = -(E)*(U) - (X) dU = (U**2)*(V) -(E+1)*(U) - (B)*(X) dV = (E)*(U) - (U**2)*(V) array_t = [0] array_X = [0] array_Y = [0] array_U = [0] array_V = [0] while t <= t_trial: X_1 = X + (dX)*(t_step/2) Y_1 = Y + (dY)*(t_step/2) E_1 = E + (dE)*(t_step/2) U_1 = U + (dU)*(t_step/2) V_1 = V + (dV)*(t_step/2) dX_1 = (A) - (B+1)*(X_1) + (X_1**2)*(Y_1) dY_1 = (B)*(X_1) - (X_1**2)*(Y_1) dE_1 = -(E_1)*(U_1) - (X_1) dU_1 = (U_1**2)*(V_1) -(E_1+1)*(U_1) - (B)*(X_1) dV_1 = (E_1)*(U_1) - (U_1**2)*(V_1) X_2 = X + (dX_1)*(t_step/2) Y_2 = Y + (dY_1)*(t_step/2) E_2 = E + (dE_1)*(t_step/2) U_2 = U + (dU_1)*(t_step/2) V_2 = V + (dV_1)*(t_step/2) dX_2 = (A) - (B+1)*(X_2) + (X_2**2)*(Y_2) dY_2 = (B)*(X_2) - (X_2**2)*(Y_2) dE_2 = -(E_2)*(U_2) - (X_2) dU_2 = (U_2**2)*(V_2) -(E_2+1)*(U_2) - (B)*(X_2) dV_2 = (E_2)*(U_2) - (U_2**2)*(V_2) X_3 = X + (dX_2)*(t_step) Y_3 = Y + (dY_2)*(t_step) E_3 = E + (dE_2)*(t_step) U_3 = U + (dU_2)*(t_step) V_3 = V + (dV_2)*(t_step) dX_3 = (A) - (B+1)*(X_3) + (X_3**2)*(Y_3) dY_3 = (B)*(X_3) - (X_3**2)*(Y_3) dE_3 = -(E_3)*(U_3) - (X_3) dU_3 = (U_3**2)*(V_3) -(E_3+1)*(U_3) - (B)*(X_3) dV_3 = (E_3)*(U_3) - (U_3**2)*(V_3) X = X + ((dX + 2*dX_1 + 2*dX_2 + dX_3)/6) * t_step Y = Y + ((dX + 2*dY_1 + 2*dY_2 + dY_3)/6) * t_step E = E + ((dE + 2*dE_1 + 2*dE_2 + dE_3)/6) * t_step U = U + ((dU + 2*dU_1 + 2*dY_2 + dE_3)/6) * t_step V = V + ((dV + 2*dV_1 + 2*dV_2 + dE_3)/6) * t_step dX = (A) - (B+1)*(X) + (X**2)*(Y) dY = (B)*(X) - (X**2)*(Y) t_step = .01 / (1 + dX**2 + dY**2) ** .5 t = t + t_step array_X.append(X) array_Y.append(Y) array_E.append(E) array_U.append(U) array_V.append(V) array_t.append(t) where previously display_x = raw_input("Choose catalyst you wish to analyze in the phase/field diagrams (X, Y, E, U, or V) ") display_y = raw_input("Choose one other catalyst from list you wish to include in phase/field diagrams ") coupledBrusselator(A, B, t_trial, display_x, display_y) Thanks!

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  • writing header in csv python with DictWriter

    - by user248237
    assume I have a csv.DictReader object and I want to write it out as a csv file. How can I do this? I thought of the following: dr = csv.DictReader(open(f), delimiter='\t') # process my dr object # ... # write out object output = csv.DictWriter(open(f2, 'w'), delimiter='\t') for item in dr: output.writerow(item) Is that the best way? More importantly, how can I make it so a header is written out too, in this case the object "dr"s .fieldnames property? thanks.

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  • Extract strings in python

    - by shadyabhi
    Basically, I want to extract the strings "AAA", "BBB", "CCC", "DDD" from a text file.. ...... (other text goes here)..... <TD align="left" class=texttd><font class='textfont'>AAA</font></TD> ..... (useless text here)..... <TD align="left" class=texttd><font class='textfont'>BBB</font></TD> ....(more text)..... <TD align="left" class=texttd><font class='textfont'>CCC</font></TD> <TD align="left" class=texttd><font class='textfont'>DDD</font></TD> ......(more text)..... I want something like if I do:- data = foo("file.txt") i get:- data = ['AAA','BBB','CCC','DDD'] What is the best possible way? My file is not big..

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  • python multithreading for dummies

    - by albruno
    trying to find a simple example that clearly shows a single task being divided for multi-threading. Quite frankly... many of the examples are overly sophisticated thus.... making the flow tougher to play with... anyone care to share their breakthrough sample or point to an example? As well, what is the best docs? many google lookups are too specific (for me at this stage) Thanks in advance.

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  • wx Python is not properly drawing customtree items

    - by uberjumper
    Hi, I am currently using wx.CustomTree, to use to display a series of configuration settings. I generally fill them with wx.TextCtrl / wx.Combobox, to allow the user to edit / enter stuff. Here is my code: class ConfigTree(CT.CustomTreeCtrl): """ Holds all non gui drawing panel stuff """ def __init__(self, parent): CT.CustomTreeCtrl.__init__(self, parent, id = common.ID_CONTROL_SETTINGS, style = wx.TR_DEFAULT_STYLE | wx.TR_HAS_BUTTONS | wx.TR_HAS_VARIABLE_ROW_HEIGHT | wx.TR_SINGLE) #self.HideWindows() #self.RefreshSubtree(self.root) self.population_size_ctrl = None self.SetSizeHints(350, common.FRAME_SIZE[1]) self.root = self.AddRoot("Configuration Settings") child = self.AppendItem(self.root, "Foo", wnd=wx.TextCtrl(self, wx.ID_ANY, "Lots Of Muffins")) The problem is, any children nodes, the data for these nodes is not filled in. When i basically expand the configuration settings tree node. I see the "Foo" node, however the textbox is empty. This is the same for both text node, Until i actually click on the child node. I've looked tried every form of update / etc. Does anyone have any ideas?

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  • Parsing specific numeric data from csv file using python

    - by KJ Lim
    Good morning. I have series of data in cvs file like below, 1,,, 1,137.1,1198,1.6 2,159,300,0.4 3,176,253,0.3 4,197,231,0.3 5,198,525,0.7 6,199,326,0.4 7,215,183,0.2 8,217.1,178,0.2 9,244.2,416,0.5 10,245.1,316,0.4 I want to extract specific data from second column for example 217.1 and 245.1 and have them concatenated into a new file like, 8,217.1,178,0.2 10,245.1,316,0.4 I use cvs module to read my cvs file, but, I can't extract specific data as I desire. Could anyone kindly please help me. Thank you.

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  • [Python] - Getting data from external program

    - by Kenny M.
    Hey, I need a method to get the data from an external editor. def _get_content(): from subprocess import call file = open(file, "w").write(some_name) call(editor + " " + file, shell=True) file.close() file = open(file) x = file.readlines() [snip] I personally think this is a very ugly way. You see I need to interact with an external editor and get the data. Do you know any better approaches/have better ideas?

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  • getting expat to use .dtd for entity replacement in python

    - by nicolas78
    I'm trying to read in an xml file which looks like this <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE dblp SYSTEM "dblp.dtd"> <dblp> <incollection> <author>Jos&eacute; A. Blakeley</author> </incollection> </dblp> The point that creates the problem looks is the Jos&eacute; A. Blakeley part: The parser calls its character handler twice, once with "Jos", once with " A. Blakeley". Now I understand this may be the correct behaviour if it doesn't know the eacute entity. However, this is defined in the dblp.dtd, which I have. I don't seem to be able to convince expat to use this file, though. All I can say is p = xml.parsers.expat.ParserCreate() # tried with and without following line p.SetParamEntityParsing(xml.parsers.expat.XML_PARAM_ENTITY_PARSING_ALWAYS) p.UseForeignDTD(True) f = open(dblp_file, "r") p.ParseFile(f) but expat still doesn't recognize my entity. Why is there no way to tell expat which DTD to use? I've tried putting the file into the same directory as the XML putting the file into the program's working directory replacing the reference in the xml file by an absolute path What am I missing? Thx.

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  • Copy string - Python

    - by Francisco Aleixo
    Ok guys I imagine this is easy but I can't seem to find how to copy a string. Simply COPY to the system like CTRL+C on a text. Basically I want to copy a string so I can for example, lets say, paste(ctrl+v). Sorry for such a trivial question, haha.

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  • python unittest howto

    - by zubin71
    I`d like to know how I could unit-test the following module. def download_distribution(url, tempdir): """ Method which downloads the distribution from PyPI """ print "Attempting to download from %s" % (url,) try: url_handler = urllib2.urlopen(url) distribution_contents = url_handler.read() url_handler.close() filename = get_file_name(url) file_handler = open(os.path.join(tempdir, filename), "w") file_handler.write(distribution_contents) file_handler.close() return True except ValueError, IOError: return False

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