Python3 Cheat Sheet

A Programming › Python cheat sheet in English by hahahaha

Basic Cheat Sheet for Python 3

17,677 views 4,434 downloads 23 Apr 2019 History

PRs

4.9 avg · 2 ratings

Lists

Create an empty list	newlist=[]
Assign value at index	alist[index]= value
Access value at index	alist[index]
Add item to list	alist.append(new item)
Insert into list	alist.insert(at position, new item)
Count # of an item in list	alist.count( item )
Delete 1 matching item	alist.remove(del item)
Remove item at index	del alist[index]

Looping

For loop 0 thru 9	for x in range(10):
For loop 5 thru 10	for x in range(5,11):
For each char in a string	for char in astring:
For items in list	for x in alist:
For indexes/values in a list	for index,value in enumerate(alist):
For each key in a dict	for x in adict.keys():
For all items in dict	for key,value in adict.items():
while <logic test>	do:
Exit loop immediately	break
Skip rest of loop and do loop again	continue

Logic and Math Operators

Math Operator	Example	X=7, Y=5
Addition	X + Y	12
Subtraction	X - Y	2
Multiplication	X * Y	35
Division	X / Y	1.4
Floor	X // Y	1
Exponent	X ** Y	16807
Modulo	X % Y	2
Logic Operator
Equality	X == Y	False
Greater Than	X > Y	False
Less Than	X < Y	True
Less or Equal	X <= Y	True
Not Equal	X !=Y or X<>Y	True
Bitwise Exclusive Or	a ^ b xor(a, b)

Converting Data Types

Covert	Syntax	Example	Result
Num -> string	str(number) int, float or long	str(100) str(3.14)	'100' '3.14'
Encoded bytes -> string	str(txt,encoding)	str(data,"utf8")	string with data
Num String -> int	int("string",base) default base is 10	int("42") int("101",2) int("ff", 16)	42 5 255
int -> hex string	hex(integer)	hex(255) hex(10)	'0xff' '0xa'
integer -> binary string	bin(integer)	bin(5) bin(3)	'0b101' '0b11'
float -> integer	int(float) drops decimal	int(3.14159) int(3.9)	3 3
int or str -> float	float(int or str)	float("3.4") float(3)	3.4 3.0
String -> ASCII	ord(str)	ord("A") ord("1")	65 49
int -> ASCII	chr(integer)	chr(65) chr(49)	'A' '1'
bytes -> string	<bytes>.decode()	b'ABC'.decode()	'ABC'
string -> bytes	<str>.encode()	'abc'.encode()	b'abc'

Useful OS functions

import os
Executing a shell command	os.system()
Rename the file or directory src to dst	os.rename(src, dst)
Change working directory	os.chdir(path)
Get the users environment	os.environ()
Returns the current working directory	os.getcwd()

Dictionaries

Create an empty dict	dict={}
Initialize a non-empty dictionary	dict= { “key”:”value”,”key2”:”value2”}
Assign a value	dict[“key”]=”value”
Determine if key exists	"key" in dict
Access value at key	dict[“key”], dict.get(“key”)
Iterable View of all keys	dict.keys()
Iterable View of all values	dict.values()
Iterable View of (key,value) tuples	dict.items()

Slicing and Indexing

x[start:stop:step]	x=[4,8,9,3,0]	x=”48930”
x[0]	4	‘4’
x[2]	9	'9'
x[:3]	[4,8,9]	'489'
x[3:]	[3,0]	'30'
x[:-2]	[4,8,9]	'489'
x[::2]	[4,9,0]	‘490’
x[::-1]	[0,3,9,8,4]	‘03984’
len(x)	5	5
sorted(x)	[0,3,4,8,9]	['0','3','4','8','9']

Misc

**Adding Comments to code:**
#Comments begin the line with a pound sign

**Adding Multi-line Comment to code**
"""
Multi-Line Comment
"""

**Get user input from keyboard**
name = input("What is your name? ")

**Functions**
def add(num1, num2):
     #code blocks must be indented
     #each space has meaning in python
     myresult = num1 + num2
     return myresult

**if then else statements**
if <logic test 1>:
     #code block here will execute
     #when logic test 1 is True
elif <logic test 2>:
     #code block executes if logic test 1 is
     #False and logic test 2 is True
else:
     #else has no test and executes when if
     #and all elif are False

**python3 shebang**
#!/usr/bin/env python3

Printing

Standard print	print('{}'.format(STRING))
Print string variable	print ("I am %s" % name)
Print int variable	print ("I am %d" % number)
Print with +	print ("I am " + name)

String Operations

Make lowercase	"Ab".lower()="ab"
Make UPPERCASE	"Ab".upper()="AB"
Make Title Format	"hi world".title()="Hi World"
Replace a substring	"123".replace('2','z')= "1z3"
Count occurrences of substring	"1123".count("1")=2
Get offset of substring in string	"123".index("2")=1
Detect substring in string	“is” in “fish” == True

Badges

Nice Cheat Sheet Good Cheat Sheet Downloaded from Unusual Locations × 1

Comments

No comments yet.