Python Cheat Sheet

SYNTAX

Escape chars

\\ Backslash (\)

\' Single-quote (')

\" Double-quote (")

\a ASCII bell (BEL)

\b ASCII backspace (BS)

\f ASCII formfeed (FF)

\n ASCII linefeed (LF)

\N{name} Character named name in the Unicode database (Unicode only)

\r Carriage Return (CR)

\t Horizontal Tab (TAB)

\uxxxx Character with 16-bit hex value xxxx (Unicode only)

\Uxxxxxxxx Character with 32-bit hex value xxxxxxxx (Unicode only)

\v ASCII vertical tab (VT)

\ooo Character with octal value ooo

\xhh Character with hex value hh

multi-line print

print '''

some stuff here

and here and here

and here

'''

print large int with space separators

var = 12000000000000
var2 = 12_000_000_000_000
print(type(var))
print(type(var2))
## int, int

STRINGS

print substring

myString = "Hello There"

print myString   # full string

print myString[0]  # print 1st char

print myString[2:5]  # print 3rd to 5th char

print string 10 times

print "hello" * 10

print multi line string

print """ stuff here stuff here

stuff here stuff here

stuff here

"""

Split string into array

var = "dog:cat:rabbit"

print var.split(':')

['dog', 'cat', 'rabbit']

Strip prefix and postfix characters

'red and blue balloon'.strip('red loon')

and blue bal

Partition a string into variables

file = 'somefile.csv'

filename, __, ext = file.rpartition('.')

Combine a string and int (concat)

log_file = logdir+'%d' % number+'.log'

remove all whitespaces

myString = ' '.join(myString.split()

remove last word from a string by delimeter

path = '/etc/network/sysconfig/ifcfg'

print path.rsplit('/', 1)[0]

>> /etc/network/sysconfig

replace whitespace with dash

myString = myString.replace(" ", "-")

remove/replace pattern from string

string = "Godzilla is a sea monster"

new = "green"

print string.replace("sea", new)

>> Gozilla is a green monster

replace everything after certain character,

string = "these pretzels are...making me thirsty!"

print string.split("...", 1)[0]

>> these pretzels are

replace string in-file

# cleanup double quotes inside file

with open(data_dir + 'file1.json') as file:

    data = file.read()

    content = data.replace('"[', '[').replace(']"', ']')

with open(data_dir + '/file1.json', 'w+') as file:

    file.write(content)

remove all text between 2 anchors in a file

xxxx

Starts with, Ends with

string = "tiger is orange"

print string.startswith("tiger")  # True

print string.endswith("green")  # False

check if string starts with a number

string = '345 broad street'

if not string[0].isdigit():

   print('does not start with number')

Lowercase, Uppercase

myString = myString.lower()  or upper()

convert all elements in List into lower or upper

myList = ['Joe', 'MARY', 'fred', 'JaNE']

myList = [x.lower() for x in myList]

>> ['joe', 'mary', 'fred', 'jane']

capitalize 1st letter

print 'charles'.title() # Charles

remove special chars

summary = re.sub('[!~`".,;:}?/\\\|={@#$%^&%*()_+<>\[\]]', '-', summary)

print multiple variables within string

print("hello there {0}, and {1} and also {2}".format("Joe", "Fred", "Mary")

>> hello there Joe, and Fred and also Mary 

remove leading,        trailing spaces,      both leading and trailing

myString.rstrip()  or lstrip()         or strip()

print string in reverse order

string = "Apples"

print string[::-1]

>> selppA

remove last character from string

str = 'abcdef,'

print str[:-1]

>> abcdef

extract word from string by delimiter

string = '/opt/my/dir/hello'

string = string.split('/')[-1]  // hello

Convert Type

List to String 

str = ''.join(myList)

String to list

str = 'black green blue'

str = str.split()

// str = ['black', 'green', 'blue']

Unicode to string

word = u'apple'

word = word.encode('utf8')

OR 

word = str(word)

String to Int

var = '3'

print type(var)

>> str

var = int(var)

print type(var)

>> int

INPUT

get input from cmd line

age = raw_input("how old are you?")

print "your age is %s" % age

get variables into script from user input

from sys import argv

script, first, second = argv

print "script is called ", script

print "first variable is ", first

print "second variable is ", second

read json from cmd line

cmd to generate json | python -c 'import sys, json; print json.load(sys.stdin)["key"]["subkey"]'

FILE HANDLING

open file for reading

file = "somefile.txt"

content = open(file)

print content.read()

open file for reading & writing

file = "somefile.txt"

content = open(file, 'rw')

content.write("new stuff here")

content.close() # close file

Better Method:

with open("myFile.txt") as file:

    data = file.read()

file = "answer.txt"

content = open(file, 'r+')

print "i is %s" % i

var = str(i)  # convert int to str

content.write(var)

content.close()

check if file exists

if os.path.exists(file_name):

  print "exists"

check if file is a file or directory

for file in glob.glob('/etc/'):

   if os.path.isdir(file):

      print('is a directory')

save incoming Json into file (create file if not there)

import json

data = request.get_json()

with open(base_dir+'/fields.json','w+') as f:

   json.dump(jsonfile,f)

append a Dict to JSON file

  output = {}
  if not os.path.exists(base_dir + "/output.json"):

       with open(base_dir + "/output.json", "w+") as f:

           json.dump(output, f)

   else:

       with open(base_dir + "/output.json", "r+") as f:

           data = json.load(f)

           data.update(output)

           f.seek(0)

           json.dump(data, f)

compare 2 files for difference

diff = difflib.ndiff(open(file1).readlines(),open(file2).readlines())

log.info(''.join(diff))

delete file

os.remove(file_path)  # file_path = /tmp/myfile.txt

rename a file

os.rename('oldName.txt', 'newName.txt')

get file checksum

from hashlib import md5

def md5checksum(filePath):

    with open(filePath, 'rb') as fh:

        m = md5()

        while True:

            data = fh.read(8192)

            if not data:

                break

            m.update(data)

        return m.hexdigest()

print md5checksum('/tmp/file1')

browse a directory, show all files, get filename, extension and parent folder

OS

change to a different dir

os.chdir( path )

print working dir

os.getcwd()

print Python path (where Modules are stored)

import sys

print sys.path

check if file exists 

if not os.path.exists(base_dir+'/fields.json'):

    do something

delete file

os.remove(filename)

copy file

from shutil import copy2

copy2(source_file, target_file)

make a directory

if not os.path.exists(log_dir):

   os.makedirs(log_dir)

print environment variable

print os.environ['ENV']

get parent directory of the py script

from inspect import getsourcefile

base_dir = os.path.dirname(getsourcefile(lambda:0))

### another way
import pathlib
base_dir = pathlib.Path().absolute()

HTTP & CURL

make a Curl request with authentication

import requests

url = "https://"+server+"/rest/api"

req = requests.get(url,auth=("username","pw),verify=False)

jsonfile = req.json()

LOGGING

basic logger

# common.py

log_dir = 'log/'

if not os.path.exists(log_dir):

    os.makedirs(log_dir)

log_file = log_dir + 'disco.log'

global log

log_format = "%(asctime)s [%(levelname)s] %(message)s"

log = logging.getLogger('myLogger')

# 5MB max, 3 files max before rollover

handler = RotatingFileHandler(log_file, maxBytes=5242880, backupCount=3)

formatter = logging.Formatter(log_format)

handler.setFormatter(formatter)

log.addHandler(handler)

log.setLevel(logging.DEBUG)

# another.py

from common import log

log.info('test log entry')

To log to both File and Syslog (with Tag)

def init_log(pluginpath):

    ''' configures Logging for each plugin '''

    log_dir = base_dir + '/logs'

    if not os.path.exists(log_dir):

        os.makedirs(log_dir)

    if pluginpath == 'maestro':

        plugin = 'maestro'

    else:

        plugin = pluginpath.split('/')[-1]

    # set level to DEBUG for trace logging

    #logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)

    # logging globals

    formatter = logging.Formatter("TagName: myApp - %(asctime)s [%(levelname)s] "+plugin+": %(message)s")

    log = logging.getLogger(plugin)

    log.setLevel(logging.ERROR)

    # set Syslog handler

    from logging.handlers import SysLogHandler

    syslog_handler = SysLogHandler(address='/dev/log')

    syslog_handler.setLevel(logging.ERROR)

    syslog_handler.setFormatter(formatter)

    log.addHandler(syslog_handler)

    # set file log handler

    from logging.handlers import RotatingFileHandler

    file_handler = RotatingFileHandler(log_dir+'/'+plugin+'.log', maxBytes=2000000, backupCount=2)

    file_handler.setFormatter(formatter)

    file_handler.setLevel(logging.DEBUG)

    log.addHandler(file_handler)    

    #log.propagate = 1

    return log

to log just to syslog

log = logging.getLogger(__name__)

log.setLevel(logging.DEBUG)

handler = logging.handlers.SysLogHandler(address = '/dev/log')

formatter = logging.Formatter('%(module)s.%(funcName)s: [%(levelname)s] %(message)s')

handler.setFormatter(formatter)

log.addHandler(handler)

PIP & PIPENV

configure pip to work behind proxy and not use SSL

mkdir ~/.config/pip

vim ~/.config/pip/pip.conf

[global]

proxy="http://proxyserver.yourcompany.com:8080"

index-url="http://pypi.python.org/simple"

trusted-host=pypi.python.org

Install via proxy & no SSL check

sudo pip install --proxy $PROXY --trusted-host pypi.python.org pylzma

pip install <pkg> config --global http.sslVerify false --proxy http://<hostname>:<port>

if getting "non existent path" error

PIPENV (new and improved pkg handler)

install pipenv

pip install --user pipenv

start new project

cd /home/user && pipenv install

install dependencies from requirements file

pipenv install -r requirements.txt

start Pipenv virtual env

pipenv shell  (type 'exit' to leave virtual env)

run a script w/o switching to shell

pipenv run python myscript.py

generate Lock file (willl force same packages for all users)

pipenv lock

generate a setup.py file from all current variables

pipenv install -e .

remove all modules installed outside of Lock file

pipenv clean

remove virtual environment

pipenv --rm

show all installed packages in virtual env

pipenv graph

install specific python version

pipenv --python 3.9 install <pkg>

install libs to a specific location
export WORKON_HOME=/home/user/venvs"
pipenv install <pkg> (will install to venvs folder)

Virtual ENV

start venv

virtualenv venv
source venv/bin/activate

stop venv
deactivate

JSON

convert multidimensional Dictionary to Json

import json
employee = {}

employee['joe'] = { 'id': 5, 'city':'boston' }
json_object = json.dumps(employee)
print(json_object)

{"joe": {"city": "boston", "id": 5}}

traverse JSON data object

json_object = {"joe": {"city": "boston", "id": 5}}

data = json.loads(json_object)

for name in data:

    print name

    print data[name]['id']

    print data[name]['city']

open json file for reading

with open('file.json') as json_data:

    data = json.load(json_data)

    print data['somevalue']

pretty print large JSON file from cmd line, 

cat file.json | python -m json.tool

YAML

open and read YAML file

with open(feed_file, "r") as file:

try:

    data = yaml.safe_load(file)

except yaml.YAMLError as e:

    print(str(e))

REGEX

import re

find string between 2 patterns

string = "{font color=red}Mary had a little lamb{/font}"

text = re.search("}(.*){", string).group(1)

>> Mary had a little lamb

string wildcard

import fnmatch

for file in os.listdir('.'):

    if fnmatch.fnmatch(file, '*.txt'):

        print file

EXCEPTIONS & DEBUG

Read in json, if fails, ignore

try: json_object = json.loads(myjson)

except ValueError, e: pass

run script with full debug

python -m trace -t script.py

print literal parameter name, not value

data = { "name": "Joe" }
value = data['name]

DATA TYPES

get type of an object

a = 'bird'

b = 5

c = ['blue', 'gray', 'yellow']

d = { 'name' : 'fred', 'id' : 3499, 'dept' : 'sales' }

type(a)  # string

type(b)  # int

typc(c)  # list

type(d)  # dict

# check if variable is certain type (returns True/False)

var = "Banana"
isinstance(var, str)  # true

isinstance(var, int)  # false

cycle through a count

import itertools
count = 0

for i in itertools.cycle("A,B,C"):

if count > 7:

break

else:

print(i)
count += 1
>>> A B C A B C A

sum up all elements of array sequentially

data = [5, 2, 6, 4, 5, 9, 1]
result = itertools.accumulate(data)
for num in result:

print(num)
>>> 5 7 13 17 22 31 32