variables numbers strings

Sure, here’s a cheat sheet covering variables, numbers, and strings in Python:

Variables

• Definition: A variable is a name that refers to a value.
• Syntax: variable_name = value
• Naming Rules:
  • Must start with a letter or underscore (_)
  • Can contain letters, numbers, and underscores
  • Case-sensitive (myVar and myvar are different)

Numbers

1. Integers:

   • Examples: 5, -3, 0
   • No decimal point

2. Floats:

   • Examples: 3.14, -0.001, 2.0
   • Contains a decimal point

3. Complex Numbers:

   • Examples: 3+4j, 1j
   • j denotes the imaginary part

4. Basic Operations:

   • Addition: a + b
   • Subtraction: a - b
   • Multiplication: a * b
   • Division: a / b (always returns a float)
   • Floor Division: a // b (integer division)
   • Modulus: a % b (remainder of the division)
   • Exponentiation: a ** b (a raised to the power of b)

Strings

1. Definition: A sequence of characters.

   • Examples: 'hello', "world", '''multi-line string''', """multi-line string"""

2. Basic Operations:

   • Concatenation: str1 + str2
   • Repetition: str * n (repeats the string n times)
   • Length: len(str)

3. Indexing and Slicing:

   • Indexing: str[index] (starts at 0)
   • Slicing: str[start:end] (end index is exclusive)
   • Example: str[1:4] (characters from index 1 to 3)

4. String Methods:

   • str.lower(): converts to lowercase
   • str.upper(): converts to uppercase
   • str.strip(): removes whitespace from both ends
   • str.replace(old, new): replaces occurrences of old with new
   • str.split(delimiter): splits the string into a list
   • str.find(substring): returns the index of the first occurrence of substring
   • str.join(iterable): joins elements of iterable into a single string

Examples

# Variables
name = "Alice"
age = 30
pi = 3.14159

# Numbers
a = 5
b = 3.2

# Operations
sum_ab = a + b          # 8.2
product_ab = a * b      # 16.0
floor_div = a // 2      # 2
modulus = a % 3         # 2
power = a ** 2          # 25

# Strings
greeting = "Hello"
full_greeting = greeting + ", " + name + "!"  # "Hello, Alice!"
repeat_greeting = greeting * 3                # "HelloHelloHello"
length_of_name = len(name)                    # 5

# Indexing and Slicing
first_char = name[0]       # 'A'
substring = name[1:4]      # 'lic'

# String Methods
lowercase_greeting = greeting.lower()  # 'hello'
uppercase_name = name.upper()          # 'ALICE'
stripped_name = "  Alice  ".strip()    # 'Alice'
replaced_greeting = greeting.replace("H", "J")  # 'Jello'
split_greeting = full_greeting.split(", ")      # ['Hello', 'Alice!']
found_index = greeting.find("e")       # 1
joined_str = ", ".join(["apple", "banana", "cherry"])  # 'apple, banana, cherry'

This cheat sheet should cover the basics for working with variables, numbers, and strings in Python. Let me know if you need more details or examples!