Basics

In Python the indentation of code is important. Everything that is indented on the same level belongs to a block.

Variables

Variables store values.

name = "me"
age = 39

Variables can't start with a number and can't have character like % or !.

We also can't use python keywords like if,for,while...

Expressions and Statements

Expression is any code that returns a value. 1+1

A statement is an operation on a value - we are doing something with the value. print(1+1)

Comments

Everything after # is ignored and can be used as comment # This is a comment

Data types

string - name = "hans"

integer - age = 2

float - temp = 2.9

boolean - isEven = True

We can check what data type a variable has with type().

Python automatically detects type of variables.

To check if something is of type string

name = "hans"
type(name) == str

#or

isinstance(name,str)

To convert int into float we can use the class-constructor of the datatype class temp = float(2)

age = int("20") -> becomes an int

The conversion is called casting

If these conversions fail we actually get an error in the console.

Operators

assignment operator = - assigns a value to a variable

Arithmetic operators

+ #addition
- #subtraction
* #multiplication
/ #division
% #remainder
** #squared
// #floor division - does the division and rounds down to the nearet whole number

We can combine arithmetic with assignment operator

+=, *= ... age += 8 -> age = age +8

Comparison operation

a == b #- Equal
a != b  #- Not equal
a > b  #- Greater
a < b #- Smaller

Boolean operators

not - #True when false
and - # both conditions have to be true
or - # one of the conditions have to be true

or returns the first not false value otherwise it returns the last operand

print(False or 'hey') # -> 'hey'
print(True or 'hey') # -> True
print(1 or 0) # -> 1

and only evaluates the second argument if the first is true. If the first argument is falsy it returns that argument - otherwise it evaluates the seconds argument.

print(0 and 1) # -> 0
print(False and 'hey') # -> False
print('hey' and 'hi') # -> hi

Bitwise operators

& # performs binary AND
| # performs binary OR
^ # performs binary XOR
~ # performs binary NOT
<< # shift left operation
>> # shift right operation

is/in operators

is is used to compare objects and returns true if both are the same object

in is membership operator - if value is contained in list or other sequence.

Ternary operator

If-Else in one line. Allows to quickly define a conditional return True if age > 18 else False

Strings

Strings are a series of characters

"hallo"
'hallo'

We can combine/concatenate strings with + 'hallo'+'world'

For multiline string we use three

"""My
name
is
"""

String Methods

.upper() converts string into all capital letters .lower() converts string into all lower letters .title() makes first letter of each string capital

To evaluate strings .islower() .isupper() .isalpha() check if string contains only characters and is not empty .isalnum() check if string contains characters or digits and is not empty .isdecimal() check if string contains digits and is not empty .startswith()/.endswidth() check if string starts/ends with substring .replace() to replace part of string .split() split string or specific character separator .strip() trim white space from a string .join() append new letters to a string .find() find position of substring.

All these methods return the new modified string. It's not changing anything in the original string.

We also can use global functions on strings. len() - get amount of character of string in

"AU" in "BEAU" # -> TRUE

If we want to show " character in a string we need to add a backslash \

"He\"llo"

The backslash is also used to add a new line into a string "Hello\n World"

To get a specific character from a string name[1] - character at index 1 name[-1] - character at the end

To get a range we do slicing

name = "ABCDEF"
name[1:3] # -> "BC" - It stops before second index 3
name[1:] # -> "BCDEF" - Blank means it goes to the end or beginning
name[:3] # -> "AB"

Booleans

Booleans are True or False values. done = True

Numbers always return True exept 0. Even negative numbers.

if 10: # <- True
    print("yes")

Strings are only False when they are empty

To check if type of value is boolean type(value) == bool

The any() functions returns True if any element of an iterable like a List is True. any([True,False]) -> True

all() function returns True if all elements of an iterable are True.

Number datatype

Number datatype allows to create the mathematical complex number complex = 2+3j or num = complex(2,3)

To get the complex or real part of the complex number num.real num.imag

abs(-5.5) - To get the absolut value of a number round(5.5) - round to nearest integer round(5.5,1) - round to nearest decimal point.

Enums

Enums are readable names that are bound to constant values. To use Enums we have to import them.

from enum import Enum

class MyState(Enum):
    INACTIVE = 0
    ACTIVE = 1


print(State.INACTIVE)
print(STATE.ACTIVE.value)

Enums are the only way to create constants in Python.

User Input

To get the input from the user at runtime we can use input("prompt"). Execution will be stopped till the user made an input and hits Enter key.

Control statements

if statement

if condition == True:
    #Execute this

if-else statement

if condiation == True:
    # Execute if condition is true
else:
    #Execute if condition is false

Multiple condition checks

For multiple condition checks we can use elif

if condition1 == True:
    #Execute this
elif condition2 == True:
    #Execute that
elif condition3 == True:
    #Execute this
#...
else:
    #if all the others are false

Lists

List are an essential data structure in Python. It allows to hold different datatypes dogs = ["Horse","Jim",3]

With in operator we can check if an item is inside a list print("Jim" in dogs) -> True

To define an empty list emptyList = []

To reference items from lists we can use the index element0 = dogs[0]

To pick from the end of the list we use - lastElement = dogs[-1] secondToLast = dogs[-2]

To update an item in a list dogs[2] = "hans"

To extract parts of the list we can use slicing firstTwoElements = dogs[:2] This returns a slice of the list

len(dogs) counts how many elements a list has.

To add items to a list we can use the .append() method. dogs.append("Ruff")

To combine two lists together we can use .extend() allDogs = dogs.extend(['hallo',"Ruofo",True])

Another way is to use += dogs += ["freaky",23]