 We evaluated Stack Overflow for the most frequent problems encountered by people & summarized the answers as well.

1. How do I check if a file exists, using Python, without using a try statement?

(compatible with python 2.x/3)

import os

print os.path.isfile(fname)

2. Best way to check if a list is empty

(2.x/3)

li=[]

if not li:

print “empty"

3. Nicest way to pad zeros to string

(2.7/3.x compatible)

“12345”.zfill(10)

4. How to know if an object has an attribute in python

hasattr(a,’attributename’)

(2.7/3.x compatable)

5. Catch Multiple Exceptions in one line

(>2.6)

except (Exception1, Exception2) as e:

pass

6. How to list all files of a directory in python ?

(2.7/3 compatible)

import os

os.listdir()

7. How do i sort a list of Dictionaries by values of Dictionaries ?

(python 2.x and 3.x compatible)

newlist = sorted(list_to_be_sorted, key=lambda k: k['name'])

8. How do you split a list into evenly sized chunks ?

def chunks(l, n):

""" Yield successive n-sized chunks from l. """

for i in xrange(0, len(l), n):

yield l[i:i+n]

9. How do i download a file over HTTP ?

import urllib2

10. Matrix multiplication in Python?

(2.x)

def matmult(a,b):

zip_b = zip(*b)

return [[sum(ele_a*ele_b for ele_a, ele_b in zip(row_a, col_b)) for col_b in zip_b] for row_a in a]

11. list all primes below N

(2.x)

def primes(n):

""" Returns  a list of primes < n """

sieve = [True] * n

for i in range(3,int(n**0.5)+1,2):

if sieve[i]:

sieve[i*i::2*i]=[False]*((n-i*i-1)/(2*i)+1)

return  + [i for i in xrange(3,n,2) if sieve[i]]

12. Binary search algorithm in python

def binary_search(array, target):

lower = 0

upper = len(array)

while lower < upper:   # use < instead of <=

x = lower + (upper - lower) // 2

val = array[x]

if target == val:

return x

elif target > val:

if lower == x:   # this two are the actual lines

break        # you're looking for

lower = x

elif target < val:

upper = x