Variables names:

• Can contain only letters ([a-zA-Z]), numbers ([0-9]), and/or underscores (_).
• Must start with a letter or underscore.
• Can't start with a number.
• Are case-sensitive.
• Can't use Python reserver keywords.

As best practices, you should use descriptive and lowercase (e.g., value) for variable names.
You should use undrscores for multi-word variable names (e.g., max_value) and use all uppercase for constants (MAX_VALUE = 10).

Define a variable:
a = "Hello" b = 1 c = False print(a) # Output: Hello print(b) # Output: 1 print(c) # Output: False
Multiple assignment: Assign multiple variable in one instruction:
x, y , z = 1, 2, 3 a, b , c = 'hello', 'python', '!'
Multiple assignment: Assign same value to multiple variables:
x = y = z = 1
Swapping variables:
x, y = 1, 2 x, y = y, x # x will have the value 2 and y will have the value 1

To comment a line or part of a line, use the hash mark character (#).
# this is a single-line comment x = 1 # this is an inline comment
For multi-line comments, use triple quotes (''', """):
""" this is a multi-line comment using triple double quotes """ ''' this is another multi-line comment using triple single quotes '''

Integers: -1, 0, 1, 2, 1_000_000, ...
Floats, 1.0, 2.0, 1.2e-3, ...
Operators: Addition (+), Subtraction (-), Multiplication (*), Division (/), Modulo (%), Exponentiation (**)

Example - Modulo operator (Remainder operator):
i = 5 % 2 print(i) # Output: 1
Using underscores for readability:
i = 1_000_000 print(i) # Output: 1000000
Complex numbers:
i = 1 + 2j print(i) # Output: (1+2j)

• Valid Strings:
  a = "This is a valid string" # double quotes c = 'This is a valid string' # single quotes b = "This is a 'valid' string" # mixed quotes d = 'This is a "valid" string' # escaped quotes
  Multi-line Strings:
  a = """This is a valid multi-line string"""
  
• Changing string case:
  
  The title() function changes each word of a string in title case (begins with a capital letter):
  print('hello python'.title()) # Output: Hello Python
  The upper() function changes a string to all uppercase:
  print('hello python'.upper()) # Output: HELLO PYTHON
  The lower() function changes a string to all lowercase:
  print('HELLO PYTHON'.lower()) # Output: hello python
  
• Formatted Strings (f-strings):
  To use a variable, expression, or a function inside a string, place the letter f before opening quotation mark.
  Inside the string put any variable or function you want to use and surround it with braces. x='hello' y='python' z=f'message: {x} {y.title()}: {2.53 * 2.98:.1f}' w=f"message: {x} {y.title()}: {2.53 * 2.98:.1f}" print(z) # Output: message: hello Python: 7.5 print(w) # Output: message: hello Python: 7.5
  You can also use the format() method:
  print("hello {}: {}".format("python", 7.5)) # Output: hello python: 7.5
  
• Adding whitespace to strings with tabs (\t) or newlines (\n): print("hello\n\n\t\tpython")
  Output:
  hello python
  
• Removing whitespace:
  
  x = ' hello python '
  Use strip() function to remove whitespace from the beginning (left) and the end (right) of a string:
  print(f'"{x.strip()}"') # Output: "hello python"
  Use lstrip() function to remove whitespace from the beginning (left) of a string:
  print(f'"{x.lstrip()}"') # Output: "hello python "
  Use rstrip() function to remove whitespace from the end (right) of a string:
  print(f'"{x.rstrip()}"') # Output: " hello python"
  
• Removing prefixes and suffixes: x = "hello.py" print(f'"{x.removeprefix("hello")}"') # Output: ".py" print(f'"{x.removesuffix(".py")}"') # Output: "hello"
  
• String splitting:
  
  
  • Split by whitespace:
    words = 'hello python 3'.split() print(f'Number of words: {len(words)} | {words}') # Output: Number of words: 3 | ['hello', 'python', '3'] for word in words: print(f'word: {word} | length: {len(word)}')
    Output:
    Number of words: 3 | ['hello', 'python', '3'] word: hello | length: 5 word: python | length: 6 word: 3 | length: 1
    
  • Split by specific delimeter:
    words = 'hello,python,3'.split(',') print(f'Number of words: {len(words)} | {words}') # Output: Number of words: 3 | ['hello', 'python', '3'] for word in words: print(f'word: {word} | length: {len(word)}')
    Output:
    Number of words: 3 | ['hello', 'python', '3'] word: hello | length: 5 word: python | length: 6 word: 3 | length: 1
    
  • Split lines:
    lines = 'hello\npython\n3'.splitlines() print(f'Number of lines: {len(lines)} | {lines}') # Output: Number of lines: 3 | ['hello', 'python', '3'] for line in lines: print(f'line: {line}')
    Output:
    Number of lines: 3 | ['hello', 'python', '3'] line: hello line: python line: 3
    
• Other methods:
  print(' '.join(['hello', 'python', '3'])) # Output: hello python 3 print('python' in 'hello python 3') # Output: True print('hello python 3'.startswith('hello')) # Output: True print('hello python 3'.endswith('3')) # Output: True print('hello python 3'.find('python')) # Output: 6 (index position) print('hello python 3'.count('o')) # Output: 2 print('hello python 3'.replace('3', '3.12.3')) # Output: hello python 3.12.3
  
• Type conversion: print(int('1')) # Output: 1 print(float('1.2')) # Output: 1.2 # handling conversion errors try: print(int('a')) except ValueError: # ValueError: invalid literal for int() with base 10: 'a' print("invalid number format") # number to string print(str(1.2)) # Output: 1.2

Parsing a date string using a specific format:
from datetime import datetime, date, timedelta, timezone # current date and time print(f'{datetime.now()}') # Output: 2023-03-29 06:19:17.217238 print(f'{date.today()}') # Output: 2023-03-29 print(f'{datetime.now().time()}') # Output: 06:19:17.217294 # specific date/time print(f'{date(2023, 3, 29)}') # Output: 2023-03-29 print(f'{datetime(2023, 3, 29, 6, 19, 17)}') # Output: 2023-03-29 06:19:17 # parsing date strings print(datetime.strptime('05/08/2023 01-16-26 PM', '%d/%m/%Y %I-%M-%S %p')) # Output: 2023-08-05 13:16:26 # formating dates (timezone) print(datetime.now(timezone.utc).strftime('%d/%m/%Y %I-%M-%S %p %z %Z')) # Output: 29/05/2023 03-38-45 PM +0000 UTC print(datetime.now(timezone(timedelta(hours=-5))).strftime('%d/%m/%Y %I-%M-%S %p %z %Z')) # Output: 29/05/2023 10-38-45 AM -0500 UTC-05:00 print(f"{datetime.now().year} - {datetime.now().month} - {datetime.now().day} - {datetime.now().hour} - {datetime.now().minute}") # Output: 2023 - 5 - 29 - 11 - 46 # date arithmetic print(date.today()) # Output: 2023-05-29 print(date.today() - timedelta(days=1)) # Output: 2023-05-28 print(date.today() - timedelta(weeks=1)) # Output: 2023-05-22 print(date(2023, 3, 29) - date(2000, 3, 29)) # Output: 8400 days, 0:00:00 print(date(2023, 3, 29) < date(2000, 3, 29)) # Output: False print(min([date(2023, 3, 29), date(2000, 3, 29)])) # Output: 2000-03-29 print(max([date(2023, 3, 29), date(2000, 3, 29)])) # Output: 2023-03-29
Date and time format codes:

• %Y: Year, in four-digit format (2023, ...)
• %y: Year, in two-digit format (23, ...)
• %m: Month number (01 - 12)
• %B: Month name (March)
• %b: Month name abbreviated (Mar)
• %d: Day of the month (01 - 31)
• %A: Weekday name (Friday)
• %a: Weekday name abbreviated (Fri)
• %H: Hour, in 24-hour format (00 - 23)
• %I: Hour, in 12-hour format (00 - 12)
• %M: Minutes (00 - 59)
• %S: Seconds (00 - 59)
• %f: Microseconds (090579)
• %p: AM|PM
• %z: UTC offset (+0000)
• %Z: Timezone name (EST)