Python Data Types int, float, str, list, dict

Python data types describe the kind of value a name currently points to: number, text, boolean, list, tuple, set, dictionary, or None.

Python keywords are reserved words that already have language meaning. You cannot use them as variable names because Python needs them for syntax.

A strong beginner skill is choosing the right data type before writing more code: one value, many ordered values, unique values, or key-value records.

Python Data Types

Python has several built-in data types. Since Python is dynamically typed, the type is determined at runtime based on the value assigned.

Category	Type	Example
Text	str	"hello", 'world'
Numeric	int, float, complex	42, 3.14, 2+3j
Boolean	bool	True, False
Sequence	list, tuple, range	[1,2,3], (1,2)
Mapping	dict	{"key": "value"}
Set	set, frozenset	{1, 2, 3}
Binary	bytes, bytearray	b"hello"
None	NoneType	None

Data Types Examples

# Numeric types
x = 42           # int
y = 3.14         # float
z = 2 + 3j       # complex

print(type(x))   # <class 'int'>
print(type(y))   # <class 'float'>
print(type(z))   # <class 'complex'>

# String
name = "Python"
print(type(name))  # <class 'str'>

# Boolean
is_active = True
print(type(is_active))  # <class 'bool'>

# None (absence of value)
result = None
print(result is None)   # True

# Sequence types
my_list  = [1, 2, 3]       # mutable
my_tuple = (1, 2, 3)       # immutable
my_range = range(1, 10, 2) # 1,3,5,7,9

# Mapping
person = {"name": "Alice", "age": 25}

# Set
unique = {1, 2, 3, 2, 1}   # {1, 2, 3}

Numeric Types

Numbers

# int - unlimited precision
big = 123456789012345678901234567890
print(big)

# float - 64-bit double precision
pi = 3.141592653589793
sci = 1.5e10   # scientific notation = 15000000000.0

# complex
c = 3 + 4j
print(c.real)  # 3.0
print(c.imag)  # 4.0
print(abs(c))  # 5.0 (magnitude)

# Useful numeric functions
print(abs(-7))      # 7
print(round(3.567, 2))  # 3.57
print(pow(2, 10))   # 1024
print(divmod(17, 5))  # (3, 2) - quotient and remainder

Python Keywords

Keywords are reserved words that have special meaning in Python. You cannot use them as variable names, function names, or identifiers.

All Python Keywords

import keyword
print(keyword.kwlist)

# Python 3 keywords:
# False    await    else     import   pass
# None     break    except   in       raise
# True     class    finally  is       return
# and      continue for      lambda   try
# as       def      from     nonlocal while
# assert   del      global   not      with
# async    elif     if       or       yield

Important Keywords

Keywords in Use

# True, False, None
flag = True
empty = None

# and, or, not
print(True and False)   # False
print(True or False)    # True
print(not True)         # False

# in, not in - membership test
fruits = ["apple", "banana"]
print("apple" in fruits)      # True
print("mango" not in fruits)  # True

# is, is not - identity test
x = None
print(x is None)       # True
print(x is not None)   # False

# del - delete a variable
temp = 42
del temp
# print(temp)  # NameError: name 'temp' is not defined

# pass - keep a block intentionally empty
def handle_later():
    pass   # add the body when the behavior is known

# assert - debugging check
age = 20
assert age >= 0, "Age cannot be negative"

Python Data Types int, float, str, list, dict

Type Basics