Python3

General

PEP 8 – Style Guide for Python Code: https://www.python.org/dev/peps/pep-0008/

Examples

Send email via SMTP:

#!/usr/bin/env python3

import smtplib
from email.message import EmailMessage

s = smtplib.SMTP('localhost')
msg = EmailMessage()

msg.set_content('Test message content')

msg['Subject'] = 'The test message'
msg['From'] = 'admin@localhost'
msg['To'] = 'example@gmail.com'

s.send_message(msg)
s.quit()

Base syntax

str(number)         # convert to string
test = 10           # init new var
test = True         # case sensitive
test = False
test_one = None     # analog 'null' (functions returns None if not return any)

print(10 == 10)     # True
== != <= >= < >
'Test' > 'Tesa'     # True (position in text, registr, position in alphabet)

del test            # del var

print("text " + str(test) + " some text")
print('hello ' * 3)         # hello hello hello (num only int)
print('hello', 3 + 4)       # hello 7

str(test)       # to string
int(test)       # to int
float(test)     # to float
list(test)      # to list

type(object)    # return class

input("input your name: ")    # return string input by keyboard

len(<string | list>)    # return length
max()                   # return max
min()

+ - * /
**      # 2 ** 3 == 8
//      # 20 // 6 == 3
%       # 20 % 6 == 2

+= -= *= /= %= **= //=

print('hello \n world')
print("hello \n world")
print('''hello
world''')
print("""hello
world""")

if test == 1 and time >= 12:
    print(test)    # tab important
elif test == 2 or (time <= 12 and date == "summer"):
    print('hah!')
else:
    print('hm..')

if not 1 < 2:        # invert
    print("yeah")    # yeah don't print

while i <= 5:
    print('ok')
    i += 1

    if i == 3:
        break

    if i == 2:
        continue    # go to next iteration

for test in range(15):
    print(test)

Lists

test = [1, 2, 3, [4, 5, 6]]

print(test[3][0])   # 4
print(test[0:2])    # 1, 2
print(test[:2])     # 1, 2
print(test[2:])     # 3, [4, 5, 6]
print(test[::2])    # all with step 2
test[start:to:step]

test = [1, 2, 3]
print(test * 2)     # [1, 2, 3, 1, 2, 3]

test = [1, 2, 3, 4, 5, 6]
print(test[-2])             # 5
print(test[::-1])           # [6, 5, 4, 3, 2, 1]

test = 'HELLO'
print(test[3])      # L

test = [1, 2, 3]
if 1 in test:       # find in list
    print('yeah')

if 1 not in test:
    print('yeah')

test.append(object)         # add to list
test.remove(object)         # find first input and remove
test.insert(pos, object)
test.count(object)
test.reverse()              # reverse list (return none)

test = range(10)
print(list(test))           # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

test = range(10, 15)
print(list(test))           # [10, 11, 12, 13, 14]

test = range(0, 10, 2)
print(list(test))           # [0, 2, 4, 6, 8]

for element in test:
    print(element)          # all elements

Tuples

Less resource pressure than LISTS

names = ("Make", "James")   # elements can't be change
names = "Make", "James"     # elements can't be change
print(names[0])

Dictionary

test = {
    "key" : "value",        # key == only simple types
    "key2" : "value2"
}
print(test["key"])                # exception if not exist
print(test.get('key'))            # return None if not exist
print(test.get('key', 'text'))    # return 'text' if not exist

if 'key' in test:
    print('OK')

if 'key' not in test:
    print('hm..')

Functions

def sum(a, b):        # DEFINE ONLY BEFORE USE
    """On line documentation"""
    return a + b

print(sum(1, 5))
print(sum.__doc__)

my_sum = sum
print(my_sum(1, 5))


def complex(real=0.0, imag=0.0):
    """Form a complex number.

    Keyword arguments:
    real -- the real part (default 0.0)
    imag -- the imaginary part (default 0.0)
    """

def incr(a):
    return a + 1

print(sum(incr, 5))     # send fuction in function

def fun(text):
    assert text != ''
    print(text)
fun('')    # AssertionError

def fun(text):
    assert text != '', "text could be no blank!"
    print(text)
fun('')    # AssertionError: text could be no blank!

# any number of args
def func(*args):
    return args # args - tuple

func(1, 2, 3, 'abc')    # (1, 2, 3, 'abc')
func()                  # ()
func(1)                 # (1,)

# any number of kv args
def func(**kwargs):
    return kwargs   # kwargs - dictionary

func(a=1, b=2, c=3)     # {'a': 1, 'c': 3, 'b': 2}
func()                  # {}
func(a='python')        # {'a': 'python'}

Modules

https://pypi.python.org/pypi http://pypi-ranking.info/alltime

# import module
import random

a = random.randint(0, 10)

# import function from module
from random import randint
from math import sqrt, pi

a = randint(0, 10)

# import all function from module
from random import *

# rename import function
from math import sqrt as my_sqrt
my_sqrt(25)

Exceptions

Catch all exceptions:

try:
    print(4 / 0)

except:
    print("oh no =(")
    raise    # show exception, exit programm

ZeroDivisionError:

try:
    print(4 / 0)

except ZeroDivisionError:
    print("Error")

Different exceptions catching:

try:
    print(4 / 0)

except ZeroDivisionError:
    print('zero division err')

except NameError:
    print('var not defined')

except SyntaxError:
    print('syntax err')    # no catch syntax err

except:
    print('some err')

Syntax error:

try:
    eval('<some code>')

except SyntaxError:
    print('Syntax error')

Finnaly:

try:
    <code>

except:
    <code>

finally:
    <code>    # run always (if catch or no catch)

Override error:

try:
    a = 1
    if a == 1:
        raise ZeroDivisionError

except ZeroDivisionError:
    print("zero division err")

a = 1
if a == 1:
   raise ZeroDivisionError('some text')        # ZeroDivisionError: some text

Own exceptions:

class MyError(Exception):
    print('hm')

raise MyError('TEST')

Files

r - read w - write (create if not exist, rewrite if exist) a - append

b - binary mode (rb wb ab)

file = open('file.txt', 'r')
print(file.read())
file.close()

# read 1 byte
file.read(1)

file = open('file.txt', 'w')
file.write('hello')
file.close()

# append
file = open('file.txt', 'a')
file.write('hello')
file.close()

# get list of lines
file.readlines()

# close file descriptor automatically
with open('file', 'r') as f:
    print(f.read())

COMMENTS

# this is a comment
print('hello')    # this is a comment

'''Multi
lines
comment'''

"""Multi
lines
comment"""

Reserved VARS

foo bar

Classes

All classes is an object of class metaclass - ‘type’.

class MyClass:
    pass        # pass do nothing

# new object of class
obj = MyClass()