freeCodeCamp/guide/english/python/data-structures/integers/index.md

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title: Python Integers
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The theoretical domain for integers in python is negative infinity to infinity. In practice, integer values are limited by the amount of available memory.

In Python 2, there was a distinction between **`int`**, numbers that fit in a 32 or 64 bit _C long_, and **`long`**, numbers limited by available memory. Python 3 unified the two types into just **`int`**, more info in <a href='https://www.python.org/dev/peps/pep-0237/' target='_blank' rel='nofollow'>PEP 237</a>.

**`int` creation using integer literals**

<a href='https://docs.python.org/3/reference/lexical_analysis.html#integer-literals' target='_blank' rel='nofollow'>Integer Literals</a>

_Integer objects_ can be created using using integer literals. Unadorned numbers without decimals are integer literals:

    >>> 1234567890           # Unadorned numbers are integer literals
    1234567890
    >>> type(1234567890)
    <class 'int'>

Numeric literals do not contain a sign, however creating negative _integer objects_ is possible by prefixing with a unary `-` (minus) operator with no space before the literal:

    >>> -1234567890
    -1234567890
    >>> type(-1234567890)
    <class 'int'>

Likewise, positive integer objects can be created by prefixing a unary `+` (plus) operator with no space before the digits. Usually `+` is ommited:

    >>> +1234
    1234

Binary (base 2, prefix: `0b` or `0B`), octal (base 8, prefix: `0o` or `0O`), and hexadecimal (base 16, prefix: `0x` or `0X`) integers can also be created using integer literals:

    >>> 0b1, 0b10, 0b11
    (1, 2, 3)
    >>> 0o1, 0o10, 0o11
    (1, 8, 9)
    >>> 0x1, 0x10, 0x11
    (1, 16, 17)

Note that leading 0's for non-zero integer literals are **not allowed**:

    >>> 0     # Zero by itself is okay.
    0
    >>> 01    # Leading zero(s) cause SyntaxError.
      File "<stdin>", line 1
        01
         ^
    SyntaxError: invalid token

The `int` <a href='https://docs.python.org/3/library/functions.html#int' target='_blank' rel='nofollow'>constructor</a> is another way to create _integer objects_.

    class int(x=0)
    class int(x, base=10)

Creating _integer objects_ with integer literals is preferred when possible:

    >>> a = 1         # Prefer integer literal when possible.
    >>> type(a)
    <class 'int'>
    >>> b = int(1)    # Works but unnecessary.
    >>> type(b)
    <class 'int'>

However, the constructor allows for creating _integer objects_ from other number types:

    >>> a = 1.123
    >>> type(a)
    <class 'float'>
    >>> print(a)
    1.123
    >>> b = int(1.123)
    >>> type(b)
    <class 'int'>
    >>> print(b)
    1

Using the `int` constructor for floating point numbers will truncate the number towards zero:

    >>> int(-1.23)
    -1
    >>> int(1.23)
    1

The built-in `boolean` constants are instances of the `bool` class, and are subclasses of the `int` class, making them a kind of numeric type:

    >>> type(True)
    <class 'bool'>
    >>> issubclass(bool, int)
    True

If that doesn't make sense to you, don't worry. For now just remember that calling the int constructor with `boolean` objects will return _integer objects_:

    >>> int(True)
    1
    >>> int(False)
    0

The `int` constructor will also make _integer objects_ from strings:

    >>> a = "10"
    >>> type(a)
    <class 'str'>
    >>> b = int("10")
    >>> type(b)
    <class 'int'>

_Strings_ for the `int` constructor must represent an integer literal:

The second parameter of the `int` constructor is to specify a base (default: 10). Valid bases are 0 and 2-36.

If an explicit base is provided the first argument must be a string.

    >>> int("111", 2)
    7
    >>> int(111, 2)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: int() can't convert non-string with explicit base

The string used for the `int` constructor with an explicit base must be a valid integer literal for that base:

    >>> int('11', 2)
    3
    >>> int('12', 2)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: invalid literal for int() with base 2: '12'

Both prefixed and non-prefixed strings of integer literals can be used, however, if used, the prefix must match the provided base.

    >>> int('1101', 2)
    13
    >>> int('0b1101', 2)
    13
    >>> int('0x1101', 2)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: invalid literal for int() with base 2: '0x1101'

If a prefixed string and base 0 is used, the created integer object will use the base specified by the prefix. If no prefix is used, then the base is assumed 10

    >>> int('100', 0)
    100
    >>> int('0b100', 0)
    4
    >>> int('0o100', 0)
    64