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  • Python constructor does weird things with optional parameters

    - by christangrant
    Can you help me understand of the behaviour and implications of the python __init__ constructor. It seems like when there is an optional parameter and you try and set an existing object to a new object the optional value of the existing object is preserved and copied. Ok that was confusing... so look at an example I concocted below. In the code below I am trying to make a tree structure with nodes and possibly many children . In the first class NodeBad, the constructor has two parameters, the value and any possible children. The second class NodeGood only takes the value of the node as a parameter. Both have an addchild method to add a child to a node. When creating a tree with the NodeGood class, it works as expected. However, when doing the same thing with the NodeBad class, it seems as though a child can only be added once! The code below will result in the following output: Good Tree 1 2 3 [< 3 >] Bad Tree 1 2 2 [< 2 >, < 3 >] Que Pasa? Here is the Example: #!/usr/bin/python class NodeBad: def __init__(self, value, c=[]): self.value = value self.children = c def addchild(self, node): self.children.append(node) def __str__(self): return '< %s >' % self.value def __repr__(self): return '< %s >' % self.value class NodeGood: def __init__(self, value): self.value = value self.children = [] def addchild(self, node): self.children.append(node) def __str__(self): return '< %s >' % self.value def __repr__(self): return '< %s >' % self.value if __name__ == '__main__': print 'Good Tree' ng = NodeGood(1) # Root Node rootgood = ng ng.addchild(NodeGood(2)) # 1nd Child ng = ng.children[0] ng.addchild(NodeGood(3)) # 2nd Child print rootgood.value print rootgood.children[0].value print rootgood.children[0].children[0].value print rootgood.children[0].children print 'Bad Tree' nb = NodeBad(1) # Root Node rootbad = nb nb.addchild(NodeBad(2)) # 1st Child nb = nb.children[0] nb.addchild(NodeBad(3)) # 2nd Child print rootbad.value print rootbad.children[0].value print rootbad.children[0].children[0].value print rootbad.children[0].children

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  • Intercept method calls in Python

    - by eaigner
    Hi. I'm implementing a RESTful web service in python and would like to add some QOS logging functionality by intercepting function calls and logging their execution time and so on. Basically i thought of a class from which all other services can inherit, that automatically overrides the default method implementations and wraps them in a logger function. What's the best way to achieve this?

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  • Getting logging.debug() to work on Google App Engine/Python

    - by brainjam
    I'm just getting started on building a Python app for Google App Engine. In the localhost environment I'm trying to send debug info to the GoogleAppEngineLauncher Log Console via logging.debug(), but it isn't showing up. However, anything sent through, say, logging.info() or logging.error() does show up. I've tried a logging.basicConfig(level=logging.DEBUG) before the logging.debug(), but to no avail. What am I missing?

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  • python webtest port configuration?

    - by MattM
    I am attempting to write some tests using webtest to test out my python GAE application. The problem I am running into is that the application is listening on port 8080 but I cannot configure webtest to hit that port. For example, I want to use app.get('/getreport') to hit http://localhost:8080/getreport. Obviously, it hits just thits http:// localhost/getreport. Is there a way to set up webtest to hit a particular port?

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  • Why is "while" loop really needed in Python?

    - by Tomaž Pisanski
    I was told that 95% of all loops in Python are "for" loops. Since "while" loops are clearly more "dangerous" than "for" loops, I would like to know if there are situations in which the use of a "while" loop is essential. For teaching purposes it would be useful to know if there is a systematic way of transforming "while" loops into "for" loops.

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  • All possible permutations of a set of lists in Python

    - by Ian Davis
    In Python I have a list of n lists, each with a variable number of elements. How can I create a single list containing all the possible permutations: For example [ [ a, b, c], [d], [e, f] ] I want [ [a, d, e] , [a, d, f], [b, d, e], [b, d, f], [c, d, e], [c, d, f] ] Note I don't know n in advance. I thought itertools.product would be the right approach but it requires me to know the number of arguments in advance

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  • Memory efficient int-int dict in Python

    - by Bolo
    Hi, I need a memory efficient int-int dict in Python that would support the following operations in O(log n) time: d[k] = v # replace if present v = d[k] # None or a negative number if not present I need to hold ~250M pairs, so it really has to be tight. Do you happen to know a suitable implementation (Python 2.7)? EDIT Removed impossible requirement and other nonsense. Thanks, Craig and Kylotan! To rephrase. Here's a trivial int-int dictionary with 1M pairs: >>> import random, sys >>> from guppy import hpy >>> h = hpy() >>> h.setrelheap() >>> d = {} >>> for _ in xrange(1000000): ... d[random.randint(0, sys.maxint)] = random.randint(0, sys.maxint) ... >>> h.heap() Partition of a set of 1999530 objects. Total size = 49161112 bytes. Index Count % Size % Cumulative % Kind (class / dict of class) 0 1 0 25165960 51 25165960 51 dict (no owner) 1 1999521 100 23994252 49 49160212 100 int On average, a pair of integers uses 49 bytes. Here's an array of 2M integers: >>> import array, random, sys >>> from guppy import hpy >>> h = hpy() >>> h.setrelheap() >>> a = array.array('i') >>> for _ in xrange(2000000): ... a.append(random.randint(0, sys.maxint)) ... >>> h.heap() Partition of a set of 14 objects. Total size = 8001108 bytes. Index Count % Size % Cumulative % Kind (class / dict of class) 0 1 7 8000028 100 8000028 100 array.array On average, a pair of integers uses 8 bytes. I accept that 8 bytes/pair in a dictionary is rather hard to achieve in general. Rephrased question: is there a memory-efficient implementation of int-int dictionary that uses considerably less than 49 bytes/pair?

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  • Python XMLRPC with concurrent requests

    - by MattB
    I'm looking for a way to prevent multiple hosts from issuing simultaneous commands to a Python XMLRPC listener. The listener is responsible for running scripts to perform tasks on that system that would fail if multiple users tried to issue these commands at the same time. Is there a way I can block all incoming requests until the single instance has completed?

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  • python programme.

    - by siva
    hi, i am siva this is frist time taken the python programming language i have a small problem please help me the question is **Write two functions, called countSubStringMatch and countSubStringMatchRecursive that take two arguments, a key string and a target string. These functions iteratively and recursively count the number of instances of the key in the target string. You should complete definitions for def countSubStringMatch(target,key): and def countSubStringMatchRecursive (target, key): **

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  • R or Python for file manipulation

    - by danspants
    I have 4 reasonably complex r scripts that are used to manipulate csv and xml files. These were created by another department where they work exclusively in r. My understanding is that while r is very fast when dealing with data, it's not really optimised for file manipulation. Can I expect to get significant speed increases by converting these scripts to python? Or is this something of a waste of time?

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  • Break the nested(double) loop in python

    - by prosseek
    I use the following method to break the double loop in Python. for word1 in buf1: find = False for word2 in buf2: ... if res == res1: print "BINGO " + word1 + ":" + word2 find = True if find: break Is there better way to break the double loop?

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