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Python

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These are my notes while taking the Complete Python Developer course by Andrei Neagoie on ZTM Academy.



Right away, I am impressed with the Python site by giving you up front details and tutorials on how to learn the language.

Python.org

Getting started with Python

Python for Programmers Tutorials

Disclaimer: I came from a JavaScript background and this will be starting from a more advanced level than someone who is new to programming. The links above do go through some more of the basics. Also, fair warning for when I start comparing things to JavaScript 😏

Python is:

  • strongly typed - types are enforced
  • dynamic - checked during execution, not before
  • implicit - variables do not need to be declared
  • object-oriented - everything is an object

Syntax

Python does not have a mandatory character (like semicolon ;) to close off a statement, the end of a statement is marked by a newline character. To continue a statement to multiple lines, use the line continuation character (\). Blocks are specified by four spaces or a tab indentation, not including the indentation will result in a syntax error. Statements that need an indentation after end in a colon (:). Failing to indent a block of code will result in a syntax error. Comments start with the pound or hashtag (#) symbol for a single line and 3 string characters (''') to start and end the block for multi-line comments. Assignment is done with the equals (=) sign, and testing equality is done with a double equals (==). You can also shortcut increment/decrement characters with (+=/-=).

a = 5 #no semicolon here
b = 2

if a > b:
    print(a 'is greater than' b)
elif a == b:
    print(a 'is equal to' b)
else:
    print(a 'is less than' b))

'''
not indenting the print line
will give a syntax error
'''
# as long as the string comment
# isn't set to a variable,
# python will ignore it

Variables

Rules for naming Python variables:

  • ◾ Must start with a letter or underscore (_) character.
  • ◾ Cannot start with a number.
  • ◾ Can only contain alpha-numeric characters and underscores.
  • ◾ Names are case-sensitive.

Multiple values can also be assigned in one line.

x, y, z = 'one', 'two', 'three'
print(x)
print(y)
print(z)

# one
# two
# three

Constants can be declared in Python using all caps and underscores (_). Constants are typically declared in a separate file and then imported back into the main file.

# constant.py
PI = 3.14
GRAVITY = 9.8

# main.py
import constant
print(constant.PI) # 3.14
print(constant.GRAVITY) # 9.8

Operators

Math Operators

  • ◾ + Addition, adds two numbers.

  • ◾ - Subtraction, subtracts two numbers.

  • ◾ * Multiplication, multiplies two numbers.

  • ◾ / Division (float), divides first number by the second number with remainders as floating point number.

  • ◾ // Division (floor), divides first number by the second number rounded to the nearest number.

  • ◾ % Modulus, returns the remainder of the first number divided by the second number.

# Examples of Arithmetic Operator
a = 9
b = 4

add = a + b
sub = a, b
mul = a * b
div1 = a / b
div2 = a // b
mod = a % b

print(add) # 13
print(sub) # 5
print(mul) # 36
print(div1) # 2.25
print(div2) # 2
print(mod) # 1

Relational Operators

  • ◾ > Greater than, returns true if left is greater than the right, else false.

  • ◾ < Less than = return true if left is less than the right, else false.

  • ◾ == Equal to, true if both sides are equal and of the same type.

  • ◾ != Not equal to, true if sides are not equal, else false.

  • ◾ >= Greater than or equal to, true if the left is greater or equal to the right.

  • ◾ <= Less than or equal to, true if the left is less than or equal to the right.

# Examples of Relational Operators
a = 13
b = 33

print(a > b) # False
print(a < b) # True
print(a == b) # False
print(a != b) # True
print(a >= b) # False
print(a <= b) # True

Logical Operators

  • ◾ and AND, true if both or all conditions are true, else false.

  • ◾ or OR, true if any condition is true, else false.

  • ◾ not NOT, true if the condition is false, else true.

# Examples of Logical Operator
a = True
b = False

print(a and b) # False
print(a or b) # True
print(not a) # False

Python also has global or local variables. Any variable created outside of a function will be global and accessible anywhere. A variable created inside of a function will be local and will only be accessible within that function. The keyword global can be used on a variable inside of a function to make it accessible from the outside or to allow changes in a function to a variable declared on the global scope.

Types

Python has many different types that are able to do different things based on their type. To get the type of a variable, you can run type(var).


Text str
Numeric: int, float, complex
Sequence: list, tuple, range
Mapping dict
Set: set, frozenset
Boolean bool
Binary: bytes, bytearray, memoryview

Example Data Type
x = "Hello World" str
x = 20 int
x = 20.5 float
x = 1j complex
x = ["apple", "banana", "cherry"] list
x = ("apple", "banana", "cherry") tuple
x = range(6) range
x = {"name" : "John", "age" : 36} dict
x = {"apple", "banana", "cherry"} set
x = frozenset({"apple", "banana", "cherry"}) frozenset
x = True bool
x = b"Hello" bytes
x = bytearray(5) bytearray
x = memoryview(bytes(5)) memoryview

Keywords

Keywords in Python
False class finally is return
None continue for lambda try
True def from nonlocal while
and del global not with
as elif if or yield
assert else import pass  
break except in raise