Python

Application

File Header

#!/usr/bin/python

Comments

These begin with the # character

Libraries

these go under the file header and in the format of

import libraryname

or

from libraryname import sublibraryname

Subroutines

These must be placed at the top, under the file header and library includes

def functionname(value):
	#do something
	return somevariable

Variables

There is no method to define a variable type, it is determined by the type of the first value it gets set to
a = 42 will create an int called a with value 42

Loops

Infinite

while True:
	#code to loop

While (check then run)

a = 0
while a < 10:
	a += 1

While (run then check)

while True:
    #code
    if i == 10:
       break	#this exits the while loop

For

for i in range(2, 10 + 1, 1):	#step from 2 to 10 by 1
	print i

for i in range(127, 0 - 1, -1):	#step from 127 to 0 by 1
	print i

Conditionals

Equal

if i == 10:
	print i

Not equal

if i != 10:
	print i

Greater than

if i > 10:
	print i

Less than

if i < 10:
	print i

Greater than or equal to

if i >= 10:
	print i

Less than or equal to

if i <= 10:
	print i

If Else

if i == 10:
	print i
else:
 	print "I isn't 10"

Math

Arithmetic functions

a = b + 2	#addition
a = b - 2	#subtraction
a = b * 2	#multiplication
a = b / 2	#division
a = b % 2	#modulo division (divides b by 2, and returns the remainder)

If the name of the variable you are setting is the same as the first parameter variable name (example: a = a + 1), then it can also be written as a += 1

Generating random values

import random

print random.randint(1, 5)	#prints a random whole number between 1 and 5

Bitwise functions

a = b >> 2	#shift the bits of an int right by an amount of times (2 in this case)
a = b << 2	#shift the bits of an int left by an amount of times (2 in this case)
a = b | 2	#sets a to all the bits in b logical ORed with all the bits in 2
a = b & 2	#sets a to all the bits in b logical ANDed with all the bits in 2
a = a ^ 2	#sets a to all the bits in b logical XORed with all the bits in 2
a = ~ b	#sets a to all the bits in b switched (0s become 1, 1s become 0)

If the name of the variable you are setting is the same as the first parameter variable name (example: a = a << 1), then it can also be written as a <<= 1

Files

Writing to a text file

with open("filename.txt", "w") as outputfile1:	#w for write, change to a for append to add to the bottom of an existing file
	outputfile1.write("Hello\r\n")	#\r\n creates a new line, so whatever is written next will be on a new line
outputfile1.close()

Read a text file, line by line

f1 = open('file.txt','r')
for line in f1:
	print line
f1.close()

Reading a binary file into an array

with open(filename.bin, mode='rb') as f1: 
	chrarray = f1.read()
f1.close()

for c in chrarray:
	bytevalue = ord(c)	#convert from a character to an int value (of the character)
	#do something

Writing to a binary file

with open(filename, mode='b') as f1:	#change b to ab for append (add data to the end of an existing file) mode
	f1.write(struct.pack('I', 123456789))	#write value as unsigned int ('I') instead of string
f1.close()

to see a full list of types, please check this link
For example, you can f1.write(struct.pack('<Q', 0x50D822A1E911F43E)) #< for little-endian, 'Q' is 8 byte unsigned long long

Check if a file exists

import os

if os.path.exists('/var/somefile.txt') == True:	#note, in windows the slashes go the other way and may contain drive letters
	#do something

Delete a file

import os

os.remove("file.txt")

Check if a character is in a file

if '.' in open('ipaddr.txt').read():
	#do something

Strings

Combining strings

print "abc" + "123"

Splitting strings (by a character)

mystring = "Hello,World"
paramlist = mystring.split(',')	#paramlist will then contain an array of 2 separate strings, ['Hello', 'World']. paramlist[0] will contain Hello and paramlist[1] will contain World and paramlist[0][1] contains e

Stepping though the characters in a string

mystring = "Hello"
for c in mystring:
	print c:

This will produce
H
e
l
l
o

Slicing

Get a specific character from a position within a string

mystring = "Hello"
print mystring[1]	#this will print the 2nd character (e) 0 is the first

Get a subsection of a string

mystring = "Hello"
printmystring[1:3+1]	#this will start at character position 1 and end at character position 3

This will produce ell

Get the start of a string

mystring = "Hello"
print mystring[:2]	#this will give you 2 characters from the string, beginning at the start (0)

This will produce He

Get the end of a string

mystring = "Hello"
print mystring[2:]	#this will start at character position 2, until the end of the string

This will produce llo

Get the last n characters of a string

mystring = "Hello"
print mystring[-2:]	#this will get the last 2 characters from the string

This will produce lo

Get all except the last n characters

mystring = "Hello"
print mystring[:-2]	#this will get all characters in the string, except the last 2

This will produce Hel

Check if a string is a digit

"5".isdigit()

Some examples
print "1".isdigit()
True

print "01".isdigit()
True

print "0.1".isdigit()
False

print "-1".isdigit()
False

print "20".isdigit()
True

print "2v".isdigit()
False

Convert a value to a string

voltage = 20
print str(voltage) + " Volts"

This will print 20 Volts

Convert a string to an integer value

day = "05"
tomorrow = int(day) + 1	# the conversion from int to string is done here
print "tomorrow will be the " + str(tomorrow) + "th"

This will produce: tomorrow will be the 6th

Convert a string to an float value

print 2 * float("3.14159")

This will output 6.28318

Remove all whitespaces (spaces, tabs etc) from the front and end of a string

print " Hello ".strip()

This becomes "Hello"

Get the length of a string

print len("Hello")

This will output 5

Time

Adding a delay

import time

time.sleep(1)	#delay 1 second
time.sleep(0.1)	#delay 0.1 seconds (100ms)

Get the current date and time

from datetime import datetime

now = datetime.now()

print now.strftime("%d/%m/%Y %I:%M:%S.%f %p")

an example of its output: 02/10/2017 11:53:34.803179 PM

Network

Check if connected to the internet

import socket

def is_connected():
    try:
        socket.create_connection(("www.google.com", 80))
    except:
	return False
    else:
	return True

Check if a network interface is up (Linux only)

import os

def is_interface_up(interface): #interface as string, returns True/False
        with open('/sys/class/net/'+interface+'/operstate') as f1:
                line=f1.readline()
        f1.close()
        statusSTR=str.strip(line)     #remove new line whitespace 
	if statusSTR=="up":
		#ifconfil will output inet addr:x.x.x.x or unspec addr:[NONE SET]
		#os.system("/sbin/ifconfig "+interface+" | grep \"inet \">ipaddr.txt")	#get the ip4 address, sbin added incase path not yet set. removed, deprecated
                os.system("/sbin/ip -4 addr | grep inet | grep " + interface + " | awk -F\" \" '{print $2}' | sed -e 's/\/.*$//'>" + scriptpath + "/ipaddr.txt")	#get the ip4 address, sbin added incase path not yet set
		if '.' in open(scriptpath + '/ipaddr.txt').read():    #check if ip address or nothing
			retval=True
			time.sleep(1)   #network intermitantly fully up before this point
		else:
			retval=False
		os.remove(scriptpath + '/ipaddr.txt')
	else:
		retval=False
	return retval

Get the local IP address of a specific interface (Linux only)

import socket
import struct
import fcntl

def get_ip_address(ifname):
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    return socket.inet_ntoa(fcntl.ioctl(
        s.fileno(),
        0x8915,  # SIOCGIFADDR
        struct.pack('256s', ifname[:15])
    )[20:24])

Get the external Internet WAN IP address of your network

import urllib, json

def get_external_ip():
	ipdata = json.loads(urllib.urlopen("http://ip.jsontest.com/").read())
	return ipdata["ip"]

Receive UDP packets

import socket

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) # Internet UDP
sock.bind(("192.168.0.2", 8080))	#the ip address of the interface you want to listen on, the port you want to listen on

while True:
	 data, addr = sock.recvfrom(1024) # buffer size is 1024 bytes	#data will contain the data bytes, addr will contain the (external) IP address it came from
	 #code here

Send UDP packets

import socket

UDP_IP = socket.gethostbyname('myawesomeserver.org')	#get IP address to send the UDP packets to
UDP_PORT = 8080

sock = socket.socket(socket.AF_INET,socket.SOCK_DGRAM) #Internet UDP

sock.sendto("Hello", (IP, port))

Raspberry PI specific

GPIO

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM) # Broadcom pin-numbering scheme
GPIO.setup(4, GPIO.OUT) #set pin as output

GPIO.output(4, GPIO.HIGH) #set the pin high

Serial

import serial

ser = serial.Serial()
ser.baudrate = 9600
ser.port = '/dev/serial0' #COM1 (or other number) in windows
ser.timeout=2

ser.open()

while True:
	serstring = ser.readline()