Methods and Attributes

In Python, an attribute is a property or value linked to an object, while a method is a callable function bound to an object. Since everything in Python is an object, even primitive types like int, float, and str have methods and attributes.

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Discovering Methods and Attributes

Use dir() to see all methods and attributes of any object:

print(dir(float))
print(dir(int))
print(dir(str))

Use help() for documentation:

help(str.upper)

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float Type

Storage: IEEE 754

Python floats are 64-bit double-precision (IEEE 754):

Component	Bits
Sign	1
Exponent	11
Mantissa	52
Total	64

mantissa_bits = 52
exponent_bits = 11
sign_bit = 1
total = mantissa_bits + exponent_bits + sign_bit
print(f"Float size: {total} bits")  # 64 bits

Precision Limitations

Floats have finite precision:

print(0.1 + 0.2)        # 0.30000000000000004 (not 0.3!)
print(0.1 + 0.2 == 0.3) # False

For exact decimals, use decimal.Decimal:

from decimal import Decimal
print(Decimal('0.1') + Decimal('0.2'))  # 0.3

Float Methods

x = 3.14

x.is_integer()          # False (not a whole number)
(4.0).is_integer()      # True

x.as_integer_ratio()    # (7070651414971679, 2251799813685248)

x.hex()                 # '0x1.91eb851eb851fp+1'

Float Attributes

x = 3.14
print(x.real)           # 3.14 (real part)
print(x.imag)           # 0.0 (imaginary part)

Comparing Floats

Use tolerance for comparison:

a = 0.1 + 0.2
b = 0.3

# Wrong
print(a == b)                   # False

# Correct
print(abs(a - b) < 1e-9)        # True

# Or use math.isclose
import math
print(math.isclose(a, b))       # True

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int Type

Storage: Arbitrary Precision

Python integers have no size limit — they grow as needed:

big = 31415926535897932384626433832795028841971693993751058209749445923078164062
print(big)
print(type(big))        # <class 'int'>

No overflow errors like in C/Java.

Integer Methods

n = 42

n.bit_length()          # 6 (bits needed to represent 42)
n.bit_count()           # 3 (number of 1s in binary: 101010)

(255).to_bytes(2, 'big')    # b'\x00\xff'
int.from_bytes(b'\x00\xff', 'big')  # 255

Integer Attributes

n = 42
print(n.real)           # 42
print(n.imag)           # 0
print(n.numerator)      # 42
print(n.denominator)    # 1

Integer Operations

print(10 // 3)          # 3 (floor division)
print(10 % 3)           # 1 (modulus)
print(divmod(10, 3))    # (3, 1) (quotient, remainder)
print(2 ** 10)          # 1024 (exponentiation)

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str Type

Storage: UTF-8 Encoding

Python strings are Unicode, encoded as UTF-8:

Character Type	Bytes	Example
ASCII	1	A, 9, !
Latin Extended	2	é, ß, ø
CJK (Korean, Chinese, Japanese)	3	안, 你, 日
Emoji	4	😊, 🚀

# ASCII string
a = "Hello"
print(len(a))                       # 5 characters
print(len(a.encode('utf-8')))       # 5 bytes

# Korean string
b = "안녕"
print(len(b))                       # 2 characters
print(len(b.encode('utf-8')))       # 6 bytes (3 per character)

# Emoji
c = "😊"
print(len(c))                       # 1 character
print(len(c.encode('utf-8')))       # 4 bytes

String Methods (Selection)

s = "Hello World"

# Case methods
s.upper()               # 'HELLO WORLD'
s.lower()               # 'hello world'
s.title()               # 'Hello World'
s.capitalize()          # 'Hello world'

# Search methods
s.find('World')         # 6 (index)
s.count('l')            # 3
s.startswith('Hello')   # True
s.endswith('World')     # True

# Modify methods
s.replace('World', 'Python')  # 'Hello Python'
s.strip()               # Remove whitespace
s.split()               # ['Hello', 'World']

# Check methods
'hello'.isalpha()       # True
'123'.isdigit()         # True
'hello123'.isalnum()    # True

String Formatting

name = "Alice"
age = 30

# f-string (recommended)
f"Name: {name}, Age: {age}"

# format method
"Name: {}, Age: {}".format(name, age)

# % formatting (old style)
"Name: %s, Age: %d" % (name, age)

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Summary: How Types are Stored

Type	Storage Format	Size	Precision
float	IEEE 754 double	64 bits	~15-17 decimal digits
int	Variable-length binary	Dynamic	Unlimited
str	UTF-8 Unicode	1-4 bytes/char	N/A

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Method Types in Classes

Python distinguishes three method types:

Instance Methods

Operate on specific instances:

class Dog:
    def __init__(self, name):
        self.name = name

    def bark(self):             # Instance method
        return f"{self.name} says woof!"

dog = Dog("Buddy")
dog.bark()                      # "Buddy says woof!"

Class Methods

Operate on the class itself:

class Dog:
    count = 0

    def __init__(self, name):
        self.name = name
        Dog.count += 1

    @classmethod
    def get_count(cls):         # Class method
        return cls.count

Dog("Buddy")
Dog("Max")
Dog.get_count()                 # 2

Static Methods

Don't depend on instance or class:

class Math:
    @staticmethod
    def add(a, b):              # Static method
        return a + b

Math.add(2, 3)                  # 5

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Key Takeaways

• Attributes: Properties/values (x.real, x.imag)
• Methods: Callable functions (x.is_integer(), s.upper())
• dir(obj) shows all methods and attributes
• float: 64-bit IEEE 754, finite precision, use Decimal for exactness
• int: Arbitrary precision, no overflow
• str: UTF-8 encoded, 1-4 bytes per character
• Python has instance methods, class methods (@classmethod), and static methods (@staticmethod)