int() Function Complexity

The int() function converts objects to integers or creates integers from strings with specified bases.

Complexity Analysis

Case	Time	Space	Notes
Convert int	O(1)	O(1)	Already integer
Convert float	O(1)	O(1)	Truncate decimal
Convert string (base 10)	O(n²)	O(n)	n = string length; quadratic for very large numbers
Convert string (other base)	O(n²)	O(n)	Parse digits; quadratic due to arbitrary precision
Convert bool	O(1)	O(1)	True→1, False→0

Basic Usage

From Numeric Types

# O(1) - type conversions
int(42)         # 42 (already int)
int(3.14)       # 3 (truncate)
int(3.99)       # 3 (truncate, not round)
int(True)       # 1
int(False)      # 0

From Strings

# O(n) - where n = string length
int("42")       # 42
int("-123")     # -123
int("0")        # 0
int("")         # ValueError

From Different Bases

# O(n) - parse digits in specified base
int("101", 2)     # 5 (binary)
int("ff", 16)     # 255 (hex)
int("77", 8)      # 63 (octal)
int("1A2B", 16)   # 6699 (hex)

Complexity Details

String Parsing

Complexity for Large Numbers

For typical small numbers (< 1000 digits), parsing is effectively O(n). For very large numbers (thousands of digits), the complexity becomes O(n²) due to arbitrary precision arithmetic during accumulation.

# O(n) for typical numbers, O(n²) for very large numbers
short = int("42")      # O(2) - effectively linear
long = int("1" * 1000) # O(1000²) for very large - quadratic

# Each character must be parsed
x = 0
for char in "12345":
    # Process each digit - O(n) total
    x = x * 10 + int(char)

Base Conversion

# O(n) - different bases same complexity
binary = int("1010101", 2)     # O(7)
octal = int("1234567", 8)      # O(7)
hex_val = int("ABCDEF", 16)    # O(6)

# Base doesn't affect complexity, just interpretation

From Float

# O(1) - just truncate
int(3.14)   # 3 - instant
int(3.99)   # 3 - instant (not rounded!)
int(-2.5)   # -2 (truncates toward zero)

Common Patterns

String to Integer Conversion

# O(n) - user input parsing
user_input = input("Enter a number: ")  # "42"
try:
    number = int(user_input)  # O(n) - parse string
    process(number)
except ValueError:
    print("Invalid integer")

Base Conversion

# O(n) - convert from different bases
hex_string = "FF"
value = int(hex_string, 16)  # O(2) - binary: 255

# Useful for configuration
config_bits = "11010110"
flags = int(config_bits, 2)  # O(8) - binary flags

List Comprehension

# O(n * m) - n items, m = avg string length
strings = ["10", "20", "30", "40"]
numbers = [int(s) for s in strings]  # O(n)
# [10, 20, 30, 40]

# With base
hex_strings = ["FF", "10", "20"]
numbers = [int(s, 16) for s in hex_strings]  # O(n)
# [255, 16, 32]

Performance Patterns

String vs Direct

# O(1) - direct
x = 42

# O(n) - string parsing
y = int("42")  # O(2)

# For performance, avoid string parsing if possible
config = 42  # Direct
value = int(config)  # O(1)

# vs
config = "42"  # String
value = int(config)  # O(n)

Batch Conversion

# O(n) - convert list of strings
data = ["1", "2", "3", "100", "200"]
numbers = [int(x) for x in data]  # O(n) total

# Using map - same complexity
numbers = list(map(int, data))  # O(n) total

Base Conversion Efficiency

# All O(n), no performance difference by base
# Time is proportional to string length, not base

# Short string, any base
int("10", 2)      # O(2)
int("10", 10)     # O(2)
int("10", 16)     # O(2)

# Long string
long_val = "1" * 1000
int(long_val, 2)  # O(1000)
int(long_val, 10) # O(1000)
int(long_val, 16) # O(1000)

Practical Examples

Parsing User Input

# O(n) - parse and validate
def get_positive_int(prompt):
    while True:
        try:
            value = int(input(prompt))  # O(n)
            if value > 0:
                return value
            print("Must be positive")
        except ValueError:
            print("Must be an integer")

# Usage
count = get_positive_int("Enter count: ")

Configuration from Strings

# O(n) - parse config values
config_str = "timeout:30,retries:3,port:8080"

def parse_config(config_str):
    config = {}
    for item in config_str.split(","):
        key, value = item.split(":")
        config[key] = int(value)  # O(m) per value
    return config

config = parse_config(config_str)
# {'timeout': 30, 'retries': 3, 'port': 8080}

Bit Manipulation

# O(n) - parse binary for bit flags
def parse_flags(binary_str):
    value = int(binary_str, 2)  # O(n)
    flags = {}
    for i, bit in enumerate(reversed(binary_str)):
        flags[f"flag_{i}"] = bool(int(bit))
    return flags

flags_str = "11010110"
flags = parse_flags(flags_str)
# {'flag_0': 0, 'flag_1': 1, 'flag_2': 1, ...}

Custom Number Base

# O(n) - support custom bases
def int_from_base(string, base):
    if base < 2 or base > 36:
        raise ValueError("Base must be 2-36")
    return int(string, base)  # O(n)

# Useful for specialized parsing
value = int_from_base("Z", 36)  # 35 in base 36
value = int_from_base("1010", 2)  # 10 in binary

Edge Cases

Empty String

# O(1) - error
try:
    int("")  # ValueError: invalid literal
except ValueError:
    pass

Whitespace

# O(n) - strips whitespace automatically
int("  42  ")     # 42 - whitespace stripped
int("\t10\n")     # 10 - tab and newline stripped

Sign Handling

# O(n) - handle negative numbers
int("-42")      # -42
int("+42")      # 42 (plus sign OK)
int("- 42")     # ValueError (space not allowed)

Large Numbers

# O(n) - Python handles arbitrary precision
big = int("999999999999999999999999999999")
huge = int("1" * 10000)  # O(10000)

# No overflow, just slower with more digits

Invalid Bases

# O(1) - check base
try:
    int("10", 1)   # ValueError: base must be >= 2
    int("10", 37)  # ValueError: base must be <= 36
except ValueError:
    pass

Comparison with float()

# int() - O(n) from string, O(1) from float
int("42")    # O(2)
int(3.14)    # O(1) - truncate

# float() - similar but handles decimals
float("3.14")  # O(4)

# int() truncates, float() keeps precision
int(3.99)   # 3
float(3.99) # 3.99

Best Practices

✅ Do:

• Validate input before converting: int(input())
• Use try-except for user input
• Specify base explicitly when parsing non-decimal: int(s, 16)
• Cache conversion results if used multiple times

❌ Avoid:

• Assuming int() won't fail on user input
• Using int() repeatedly on same string (cache it)
• Expecting int() to round (it truncates)
• Forgetting that int() parses, doesn't evaluate

Related Functions

• float() - Convert to floating-point
• str() - Convert to string
• bin() - Binary representation
• hex() - Hexadecimal representation

Version Notes

• Python 2.x: Long integers separate (long type)
• Python 3.x: Single int type with arbitrary precision
• All versions: Truncates toward zero when converting float