An Authoritative Python Cheat Sheet (WIP)

All plagiarized of course, credits at bottom..

Make the script both a module and an executable :

if __name__ == '__main__'

The __whatever__ is a "dunder" - double-underscore. There are some useful ones you'll pick up - like __init__ , __repr__ , __eq__ (that goes along with decorators), etc.

Enumerate :

for i, var in enumerate( list_name ) :
     some_useful_code using i and var

List comprehension (build a list on the fly ) :

[ x * 3 for x in data if x > 10 ]

Build a dict out of two lists :

d = dict( zip( key_list, val_list ) )

Flatten a list of lists :

>>> l_of_lists = [list(range(10)), list(range(20,30)), list(range(50,60))]
[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9], [20, 21, 22, 23, 24, 25, 26, 27, 28, 29], [50, 51, 52, 53, 54, 55, 56, 57, 58, 59]]
>>> l = [y for x in l_of_lists for y in x]
>>> l
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59]

Count number of elements in your list greater than a certain value :

sum(i > 5 for i in j)

Reverse a list :

list_name[::-1]

Parse JSON data :

import json
import requests
response = requests.get( url, params=paramDict)
parsed_json = response.json()     # then do a pprint (pretty print) to see how to use..

Pandas :

import pandas as pd
df = pd.read_csv( 'somefile.csv')
matching_list = df['field1'][df['fieldN' == 'something_specific']

import matplotlib.pyplot as plt
from matplotlib import style

style.use('classic')
df['some field'].plot()
plt.show()

To convert from JSON to dataframe :

from pandas.io.json import json_normalize
df = json_normalize( parsed_json['key name'] )

Fill out a matrix using a list or dict ( while you count from 0 to 8 generate (0,0),(0,1),(0,2),(1,0)..(2,2) )

from itertools import product

i=0
for t1, t2 in product( sorted_tags, sorted_tags ) :
    row = i // num_tags
    col = i % num_tags
    i += 1
    t_mx[row][col] = transition_counts[ (t1,t2) ]

Actually, more pythonically (maybe) :

from itertools import product

for i,j in product( range( num_tags), range(num_tags) ) :
 t_mx[i,j] = transition_counts[ (sorted_tags[i], sorted_tags[j] ) ]

QEI

http://safehammad.com/downloads/python-idioms-2014-01-16.pdf
https://coderwall.com/p/rcmaea/flatten-a-list-of-lists-in-one-line-in-python