Short (and useful) python snippets [closed]

Answer 1

Here are few which I think are worth knowing but might not be useful on an everyday basis. Most of them are one liners.

Removing Duplicates from a List

L = list(set(L))

Getting Integers from a string (space seperated)

ints = [int(x) for x in S.split()]

Finding Factorial

fac=lambda(n):reduce(int.__mul__,range(1,n+1),1)

Finding greatest common divisor

>>> def gcd(a,b):
...     while(b):a,b=b,a%b
...     return a

Answer 2

Suppose you have a list of items, and you want a dictionary with these items as the keys. Use fromkeys:

>>> items = ['a', 'b', 'c', 'd']
>>> idict = dict().fromkeys(items, 0)
>>> idict
{'a': 0, 'c': 0, 'b': 0, 'd': 0}
>>>

The second argument of fromkeys is the value to be granted to all the newly created keys.

Answer 3

Fire up a simple web server for files in the current directory:

python -m SimpleHTTPServer

Useful for sharing files.

Answer 4

For list comprehensions that need current, next:

[fun(curr,next) 
 for curr,next 
 in zip(list,list[1:].append(None)) 
 if condition(curr,next)] 

For circular list zip(list,list[1:].append(list[0])).

For previous, current: zip([None].extend(list[:-1]),list) circular: zip([list[-1]].extend(list[:-1]),list)

Answer 5

Huge speedup for nested list and dictionaries with:

deepcopy = lambda x: cPickle.loads(cPickle.dumps(x))

Answer 6

When debugging, you sometimes want to see a string with a basic editor. For showing a string with notepad:

import os, tempfile, subprocess

def get_rand_filename(dir_=os.getcwd()):
    "Function returns a non-existent random filename."
    return tempfile.mkstemp('.tmp', '', dir_)[1]

def open_with_notepad(s):
    "Function gets a string and shows it on notepad"
    with open(get_rand_filename(), 'w') as f:
        f.write(s)
        subprocess.Popen(['notepad', f.name])