Short (and useful) python snippets [closed]

Answer 1

A "progress bar" that looks like:

|#############################---------------------|
59 percent done

Code:

class ProgressBar():
    def __init__(self, width=50):
        self.pointer = 0
        self.width = width

    def __call__(self,x):
         # x in percent
         self.pointer = int(self.width*(x/100.0))
         return "|" + "#"*self.pointer + "-"*(self.width-self.pointer)+\
                "|\n %d percent done" % int(x) 

Test function (for windows system, change "clear" into "CLS"):

if __name__ == '__main__':
    import time, os
    pb = ProgressBar()
    for i in range(101):
        os.system('clear')
        print pb(i)
        time.sleep(0.1)

Answer 2

Initializing a 2D list

While this can be done safely to initialize a list:

lst = [0] * 3

The same trick won’t work for a 2D list (list of lists):

>>> lst_2d = [[0] * 3] * 3
>>> lst_2d
[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> lst_2d[0][0] = 5
>>> lst_2d
[[5, 0, 0], [5, 0, 0], [5, 0, 0]]

The operator * duplicates its operands, and duplicated lists constructed with [] point to the same list. The correct way to do this is:

>>> lst_2d = [[0] * 3 for i in xrange(3)]
>>> lst_2d
[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> lst_2d[0][0] = 5
>>> lst_2d
[[5, 0, 0], [0, 0, 0], [0, 0, 0]]

Answer 3

For Python 2.4+ or earlier:

for x,y in someIterator:
  listDict.setdefault(x,[]).append(y)

In Python 2.5+ there is alternative using defaultdict.

Answer 4

zip(*iterable) transposes an iterable.

>>> a=[[1,2,3],[4,5,6]]
>>> zip(*a)
    [(1, 4), (2, 5), (3, 6)]

It's also useful with dicts.

>>> d={"a":1,"b":2,"c":3}
>>> zip(*d.iteritems())
[('a', 'c', 'b'), (1, 3, 2)]

Answer 5

I like this one to zip everything up in a directory. Hotkey it for instabackups!

import zipfile

z = zipfile.ZipFile('my-archive.zip', 'w', zipfile.ZIP_DEFLATED)
startdir = "/home/johnf"
for dirpath, dirnames, filenames in os.walk(startdir):
  for filename in filenames:
    z.write(os.path.join(dirpath, filename))
z.close()

Answer 6

Hardlink identical files in current directory (on unix, this means they have share physical storage, meaning much less space):

import os
import hashlib

dupes = {}

for path, dirs, files in os.walk(os.getcwd()):
    for file in files:
        filename = os.path.join(path, file)
        hash = hashlib.sha1(open(filename).read()).hexdigest()
        if hash in dupes:
            print 'linking "%s" -> "%s"' % (dupes[hash], filename)
            os.rename(filename, filename + '.bak')
            try:
                os.link(dupes[hash], filename)
                os.unlink(filename + '.bak')
            except:
                os.rename(filename + '.bak', filename)
            finally:
        else:
            dupes[hash] = filename