basic types

strings

trim / strip

line.strip()

string is empty

line.strip() == ""

length of string

len(line)

string starts with

line.startswith("http")

substring

line[3:len(line)]

splitting a string on a literal separator of one or more characters

variable.split('.')

universal to string method

str(object)

escape url characters

import urllib.parse
escaped = urllib.parse.quote(string)

numbers

convert to int

int(float('14.3'))
int('15')

arrays

stack = []
stack.append('value')
for value in stack:
    print(value)

array length

len(stack)

input / output

print without newline

print(line, end="")

command line arguments

import sys
for arg in sys.argv:
    print arg

get command line argument by index

first = sys.argv[1]

count command line arguments

count = len(sys.argv)

piped input

echo -e "a\nb" | python -c '
import sys
for line in sys.stdin:
    sys.stdout.write(line)
'

write file

file = open('workfile', 'w')
file.write('This is a test\n')

read file

file = open('workfile', 'r')
contents = file.read()
print(contents)

read lines

file = open('workfile', 'r')
for line in file:
    print(line, end='')

verify directory

import os.path
if not os.path.isfile('work'):
if not os.path.isdir('work'):

create directory

import os
os.mkdir('work')

get home directory

os.getenv("HOME")

calling a shell process

import subprocess
subprocess.Popen(['/path/to/script.sh'])

calling a shell process and passing in environment variables

import os
import subprocess
variables=dict(os.environ, APPLE='PEAR')
subprocess.Popen(['/usr/bin/env'], env=variables)

ternary operator

result = [if_value] if [condition] else [else_value]

for loop with fixed iterations

for i in range(10):
	print(i)

exception handling

throw an exception

raise Exception('This user appears unequipped to use this application!')

threads

sleep

import time
time.sleep(10)

one liners

call python with script as argument

python -c 'print("hello world")'

use piped input

echo "hello world" | python -c "import sys; print(sys.stdin.read())"

use piped input line for line

echo -e "a b\r\nc d" | python3 -c 'import sys; [print(line, end="") for line in sys.stdin]'