Create matrix

Create matrix of None

A = [[ None for _ in xrange(M)] for _ in xrange(N)]

Create matrix of random numbers

import random
A = [[ random.random() for _ in xrange(M)] for _ in xrange(N)]

Generator for lists of M random elements

import random
A = ([ random.random() for _ in xrange(M)] for _ in iter(int, 1))
for i in A:
    print i
    sleep(0.2)

Flatten list of lists (only one level of nesting)

import itertools
list2d = [[1,2,3],[4,5,6], [7], [8,9]]
list(itertools.chain.from_iterable(list2d))
>>> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Strip punctuation of string

s.translate(None, string.punctuation)

Permutations

From python lexical analysis docs

def perm(l):
    # Compute the list of all permutations of l
    if len(l) <= 1:
        return [l]
    r = []
    for i in range(len(l)):
         s = l[:i] + l[i+1:]
         p = perm(s)
         for x in p:
             r.append(l[i:i+1] + x)
    return r

Print literal curly-braces

p = "{{}} {}"
p.format(7)

Random string

taken from here

import string, random
N = 7
''.join(random.choices(string.ascii_uppercase + string.digits, k=N))

cryptographically more secure version

''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits) for _ in range(N))

Show notifications on macos

From here

import os

def notify(title, text):
    os.system("""
              osascript -e 'display notification "{}" with title "{}"'
              """.format(text, title))

notify("Title", "Heres an alert")