Literals

Literals are fixed values explicitly written in code. Python supports six common literal types. String literals must be enclosed in double quotes ("), meaning any quoted text is a string.

Output literals using print():

print(42)
print(-7)
print("Greetings, Python")

Output:

42
-7
Greetings, Python

By default, print() adds a newline. Use end='' to prevent this:

print("Hi", end='')
print("World", end='')

Output: HiWorld

Comments

Comments explain code and are ignored during execution. They enhance readability.

Single-Line Comments

Start with #, followed by explanatory text (recommended to separate # and text with a space):

# Define an integer literal
42
# Define a float literal
3.14
# Define a string literal
"Greetings, Python"

# Output literals via print
print(42)
print(3.14)
print("Greetings, Python")

Output:

42
3.14
Greetings, Python

Multi-Line Comments

Enclose text in triple double quotes ("""):

"""
Demonstrates outputting literals using print statements
"""
# Output literals
print(42)
print(3.14)
print("Greetings, Python")

Output same as above.

Variables

Variables store runtime data, avoiding repetition. Their values can change. Define with variable_name = value.

Example:

# Track account balance
balance = 100
print("Current balance:", balance, "units")

# Buy coffee: spend 15 units
balance = balance - 15
print("Remaining balance:", balance, "units")

Output:

Current balance: 100 units
Remaining balance: 85 units

Data Types

Common beginner types: integers, floats, strings. Strings have three definition styles:

# Double quotes
greeting = "I am a string"
# Single quotes
message = 'I am also a string'
# Triple quotes (multi-line)
multiline_text = """I am a string
spanning multiple lines"""

print(greeting)
print(message)
print(multiline_text)

Output:

I am a string
I am also a string
I am a string
spanning multiple lines

Check types with type():

1. Direct print:

print(type("Hello"))
print(type(42))
print(type(3.14))

Output: <class 'str'>, <class 'int'>, <class 'float'>

2. Store result in variable:

str_type = type("Hello")
int_type = type(42)
float_type = type(3.14)
print(str_type, int_type, float_type)

3. Check variable-stored data type:

username = "Alice"
name_type = type(username)
print(name_type)  # <class 'str'>

Note: Variables have no inherent type; they reflect the type of stored data.

Type Conversion

Convert between types for input processing, calculations, or storage. Conversoin creates new objects; original data remains unchanged.

Common conversions:

• Any type → string: str(x)
• Numeric string → int/float: int(x), float(x) (string must contain only numbers)
• Float → int: discards decimal part

Examples:

# Number to string
str_num = str(25)
str_float = str(7.89)
print(type(str_num), str_num)  # <class 'str'> 25
print(type(str_float), str_float)  # <class 'str'> 7.89

# String to number
int_val = int("25")
print(type(int_val), int_val)  # <class 'int'> 25

# Float to int (precision loss)
int_from_float = int(12.89)
print(type(int_from_float), int_from_float)  # <class 'int'> 12

Identifiers

Identifiers name variables, classes, or functions. Follow rules and conventions.

Rules

1. Allowed characters: letters (A-Z/a-z), digits (0-9), underscores (_). No digits at start. Avoid Chinese (potential issues).
2. Case-sensitive: Age ≠ age.
3. Avoid keywords (reserved words like if, for, class).

Keyword examples (case-sensitive):

Keyword	Purpose
True/False	Boolean values
None	Null value
if/elif/else	Conditionals
for/while	Loops
def/class	Define function/class
return/yield	Return values
import/from	Module imports

Example (valid vs invalid):

# Valid
UserAge = 30
user_name = "Bob"

# Invalid (keyword)
class = 5  # SyntaxError

Conventions

• Descriptive names: account_balance over ab
• Snake_case: total_score instead of totalScore
• Lowercase letters: username, not UserName

Opertaors

Perform operations on data.

Arithmetic Operators

print(f"5 + 3 = {5 + 3}")       # 8
print(f"10 - 4 = {10 - 4}")     # 6
print(f"7 * 2 = {7 * 2}")       # 14
print(f"15 / 3 = {15 / 3}")     # 5.0
print(f"17 // 5 = {17 // 5}")   # 3 (floor division)
print(f"17 % 5 = {17 % 5}")     # 2 (modulo)
print(f"3 ** 4 = {3 ** 4}")     # 81 (exponent)

Compound Assignment Operators

count = 5
count += 3  # 8
count *= 2  # 16
count -= 4  # 12
count /= 3  # 4.0
print(count)

Input Handling

Use input() to capture keyboard input (always returns a string). Convert types as needed.

Example:

username = input("Enter your username: ")
print(f"Welcome, {username}!")

# Convert input to integer
user_age = input("Enter your age: ")
age_num = int(user_age)
print(f"Age (numeric): {age_num}, type: {type(age_num)}")

Input "Alice" then "30" outputs:

Welcome, Alice!
Age (numeric): 30, type: <class 'int'>