Data Types & Variables - CameronAuler/python-devops GitHub Wiki
Table of Contents
Variables
A named reference to a value stored in memory. Variables do not require explicit declaration and can store different data types. Python is dynamically typed, meaning you don’t need to declare the type of a variable—it’s inferred from the assigned value.
x = 10 # Integer variable
name = "John" # String variable
pi = 3.14 # Float variable
Variable Naming Rules
- Can contain letters (a-z, A-Z), digits (0-9), and underscores (_).
- Cannot start with a number.
- Cannot contain special characters like @, $, %.
- Cannot use reserved keywords (if, def, class, etc.).
- Case-sensitive (age and Age are different variables).
Valid Examples
user_name = "Alice" # Snake_case (recommended)
age = 25
MAX_LIMIT = 100 # Constants (by convention, use uppercase)
Invalid Examples
1name = "John" # ❌ Cannot start with a number
my-name = "Sam" # ❌ Hyphens are not allowed
def = 10 # ❌ Cannot use reserved keywords
Multi-variable Assignment
Python allows assigning values to multiple variables in a single line.
a, b, c = 1, 2, 3
print(a, b, c) # Output: 1 2 3
Same Value Multi-variable Assignment
x = y = z = 100
print(x, y, z) # Output: 100 100 100
Constants
A named value that cannot be modified. Python does not have a built-in constant type, but by convention, uppercase names indicate constants.
PI = 3.14159
MAX_USERS = 1000
Variable Scope & Lifetime
A variable’s scope determines where it can be accessed.
- Local Variable – Defined inside a function, accessible only within that function.
- Global Variable – Defined outside functions, accessible everywhere.
- Nonlocal Variable – Used in nested functions to refer to a variable in an enclosing function.
Local
x = 10 # Global variable
def my_function():
y = 5 # Local variable
print(y) # Accessible inside the function
print(x) # Accessible anywhere
Global
def modify_global():
global x
x = 50 # Modifies the global variable
modify_global()
print(x) # Output: 50
Numbers
Integers (int)
Includes whole numbers: positive, negative, zero, and no decimals. Python 3 has no explicit limit on the size of an integer (apart from available memory).
x = 10 # Integer
y = -5 # Negative Integer
z = 1000000 # Large Integer
print(type(x)) # Output: <class 'int'>
Floating-point numbers (float)
Numbers with a decimal point or in exponential notation. Used for real numbers (any number that can be found on the number line).
a = 10.5 # Float
b = -3.14 # Negative Float
c = 1.2e3 # Scientific notation (1.2 × 10³)
print(type(a)) # Output: <class 'float'>
Complex Numbers (complex)
A type of number that includes both real and imaginary parts. Written as a + bj, where j is the imaginary unit.
c1 = 3 + 4j
c2 = complex(2, -3) # Using the complex() function
print(c1.real) # Output: 3.0
print(c1.imag) # Output: 4.0
Strings
String Definition
Sequences of characters enclosed in quotes (' ', " ", ''' ''', """ """).
s1 = "Hello, World!" # Double quotes
s2 = 'Python is fun' # Single quotes
s3 = '''Multiline
String''' # Triple quotes for multi-line strings
String Concatenation & Repetition
name = "Python"
print(name + " Rocks!") # Concatenation
print(name * 3) # Repetition
# Output:
Python Rocks!
PythonPythonPython
String Indexding & Slicing
Strings are indexed, starting from 0 (left to right) and -1 (right to left). Slicing extracts a portion of a string.
text = "Python"
print(text[0]) # Output: 'P'
print(text[-1]) # Output: 'n' (last character)
print(text[0:3]) # Output: 'Pyt' (slicing from index 0 to 2)
String Methods
Example Variables
s = " Hello, Python! "
s_alpha = "PythonRocks"
s_digit = "12345"
s_space = " "
s_mixed = "Python123"
s_multiline = "Hello\nPython"
s_sentence = "hello, python is fun!" # Added for capitalize() method
Case Conversion
# Case Conversion
print(s.lower()) # Convert to lowercase
print(s.upper()) # Convert to uppercase
print(s_sentence.capitalize()) # Capitalize the first character
print(s_sentence.title()) # Capitalize the first character of each word
print(s.swapcase()) # Swap the case of each character
# Output:
' hello, python! '
' HELLO, PYTHON! '
'Hello, python is fun!'
'Hello, Python Is Fun!'
' hELLO, pYTHON! '
Whitespace Management
# Whitespace Management
print(s.strip()) # Remove leading/trailing whitespace
print(s.lstrip()) # Remove leading whitespace
print(s.rstrip()) # Remove trailing whitespace
print(s_space.isspace()) # Check if string contains only whitespace
# Output:
'Hello, Python!'
'Hello, Python! '
' Hello, Python!'
True
Search & Replace
# Search and Replace
print(s.replace("Python", "World")) # Replace substring
print(s.find("Python")) # Find index of first occurrence (-1 if not found)
print(s.rfind("Python")) # Find index of last occurrence
print(s.index("Python")) # Find index of first occurrence (ValueError if not found)
print(s.rindex("Python")) # Find index of last occurrence (ValueError if not found)
# Output:
' Hello, World! '
8
8
8
8
Split & Join
# Split and Join
print(s.split(",")) # Split string by delimiter
print(s.splitlines()) # Split string into lines
print("-".join(s_alpha)) # Join characters with a delimiter
# Output:
[' Hello', ' Python! ']
[' Hello, Python! ']
'P-y-t-h-o-n-R-o-c-k-s'
Check String Properties
# Check String Properties
print(s_alpha.isalpha()) # Check if all characters are alphabetic
print(s_digit.isdigit()) # Check if all characters are digits
print(s_mixed.isalnum()) # Check if all characters are alphanumeric
print(s_alpha.islower()) # Check if all characters are lowercase
print(s_alpha.isupper()) # Check if all characters are uppercase
print(s_alpha.startswith("Py")) # Check if string starts with a substring
print(s_alpha.endswith("Rocks")) # Check if string ends with a substring
# Output:
True
True
True
False
False
True
True
String Alignment
# Alignment Methods
print(s.center(20, "-")) # Center the string with padding
print(s.ljust(20, "*")) # Left-align the string with padding
print(s.rjust(20, ".")) # Right-align the string with padding
# Output:
'--- Hello, Python! ---'
' Hello, Python! ******'
'...... Hello, Python! '
Encode & Decode
# Encode and Decode
encoded = s.encode("utf-8") # Encode string to bytes
print(encoded)
print(encoded.decode("utf-8")) # Decode bytes to string
# Output:
b' Hello, Python! '
' Hello, Python! '
Count Occurrences
# Count Occurrences
print(s.count("l")) # Count occurrences of a substring
# Output:
3
String Testing
# String Testing
print(s_multiline.isprintable()) # Check if all characters are printable
print(s_alpha.isidentifier()) # Check if valid Python identifier
# Output:
False
True
Booleans and NoneType
Boolean (bool)
Boolean values are True and False (capitalized in Python). Internally, True is 1, and False is 0.
a = True
b = False
print(a + 1) # Output: 2 (True behaves as 1)
print(b * 5) # Output: 0 (False behaves as 0)
NoneType (none)
None represents the absence of a value or a null value.
x = None
print(x) # Output: None
print(type(x)) # Output: <class 'NoneType'>
Type Conversion & Casting
Implicit Type Conversion (Automatic)
Python automatically converts smaller data types to larger ones.
num_int = 5
num_float = 2.5
result = num_int + num_float # int + float → float
print(result) # Output: 7.5
print(type(result)) # Output: <class 'float'>
Explicit Type Conversion (Casting)
You can manually convert data types using built-in functions.
# Convert int to float
x = float(10)
print(x) # Output: 10.0
# Convert float to int (truncates decimal)
y = int(3.99)
print(y) # Output: 3
# Convert number to string
num = 123
str_num = str(num)
print(str_num) # Output: '123'
# Convert string to int
str_val = "456"
int_val = int(str_val)
print(int_val) # Output: 456