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Python Basics - Overview Cheat Sheet (DRAFT) by

Basic Python Sheet

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Variable Types

10
Int
 
10.0
Float
 
10 + 2j
Complex
 
"­str­ing­"
or 
'string'
String
 
(1, 2, 3)
Tuple
 
[1, 2, 3]
List
 
{'a': 1, 'b': 2, 'c': 3}
Dictionary
 
{1, 4, 5}
Set
 
True
and 
False
Booleans

Basic Functions

print(s)
Prints the string s to the screen
 
input(msg)
Prints the msg to the screen, waits for user keyboard input and returns the input as string
 
len(x)
Returns the number of elements of the sequence x
 
help(x)
Returns the help (docst­ring) of a module or function
 
eval(x)
Evaluates a string and executes it as a line of code
 
exec(x)
Evaluates a block of code in a string or a code object
 
max(x)
Returns the greatest value in a sequence
 
min(x)
Returns the smallest value in a sequence
 
type(x)
Returns the variable type of x

Variable Assignment and Operations

a = 10
Assigns 10 to a
 
b = 5
Assigns 5 to b
 
c = a + b
Evaluates a + b and assigns it to c
 
print(c)
Prints the value of c (15)

If Statements

a = 5
n = 6

if a > n**3:
    print("Is much greater")
elif a > n:
    print("Is greater")
else:
    print("Is lower")
Is lower

For Loop

a = 0

for i in range(1, 101):
    a += i

print(a)
5050

While Loop

a = 0
i = 1

while i < 101:
    a += i
    i += 1

print(a)
5050

Function

def double(x):
    return 2*x

print(double(3))
6

Function with Default Arguments

def multiply(a, b=1):
    return a * b

x1 = multiply(3, 4)
x2 = multiply(5)

print(f"x1 = {x1}")
print(f"x2 = {x2}")
x1 = 12
x2 = 5

Function - Keyword Arguments

def kword_func(a, b, c):
    print(f"a = {a}")
    print(f"b = {b}")
    print(f"c = {c}")

kword_func(c=10, a=5, b=2)
a = 5
b = 2
c = 10

Lambda Function

f = lambda x, y: x2 + x*y + y2
print(f(2, 3))
19

List Compre­hension

lc = [i**2 for i in range(6)]

print(lc)
[0, 1, 4, 9, 16, 25]

Dictionary Compre­hension

from math import factorial
dc = {i:factorial(i) for i in range(7)}
print(dc)
{0: 1, 1: 1, 2: 2, 3: 6, 4: 24, 5: 120, 6: 720}

Python Keywords

if
Starts an if statement definition
 
elseif
Tests another condition if the previous isn't True
 
else
Executes the block of code if all previous tests are False
 
and
Returns True only if both statements are True
 
or
Returns True if at least one statement is True
 
not
Returns the opposite Boolean
 
in
(on if statem­ents)
Checks if an element is in a sequence
 
is
Checks if two elements are equal to each other
 
assert
Checks a logic test and raises an error message if the test fails
 
while
Starts a while loop definition
 
for
Starts a for loop definition
 
in
(on for loop statements)
Takes each element of a sequence, one per iteration
 
continue
Skips to the next loop iteration
 
break
Exits loop statement
 
def
Starts a function definition
 
lambda
Starts a lambda function definition
 
return
Exits function and returns a value
 
yield
Used to create genera­tors. Returns a value but allows to resume the function
 
class
Starts a class definition
 
pass
Does nothing. Used where a block of text is need syntac­tically
 
from
From a module or library...
 
import
Imports a module or functi­on...
 
as
With this name...
 
try
Starts an exception handling statement
 
except
Catches an exception
 
finally
Executes at the end of the exception handling statement
 
raise
Throws an error
 
global
Make a variable global
 
local
Make a variable local
 
with
Wraps code block with methods defined by a context manager
 
del
Delete a variable from memory

Write File

a = [1, 3, 2, 5, 6, 2, 4]
b = [3, 5, 1 ,2 ,7, 7, 8]

with open('data.csv', 'w') as file:
    for i, j in zip(a, b):
        file.write(f"{i}, {j}\n")
This code writes a csv file based on the data in a and b

Read File

with open('data.csv', 'r') as file:
    for line in file:
        print(line)
This code reads the file and prints it line by line.