3. Nearly everything about numbers

3.1. The numeric types

There are 4 numeric types:

• plain integers
• long integers
• floating-point numbers
• complex numbers

The long integers are code with the letter L:

>>> 2**62
4611686018427387904
>>> 2**63
223372036854775808L

To determine the largest possible integer on your system, use:

>>> import sys
>>> sys.maxint

Complex numbers are coded using the j letter for imaginary part:

>>> a = 1 + 2j
>>> a.real
1.0
>>> a.imag
2.0
>>> a.conjugate()
(1 - 2*j)

Note that the type of the real and imaginary parts are floats becuase complex numbers use floats.

Note

cmath module provides the complex functions found in the math module

You may also use octal and hexadecimal integers. Octal starts with a zero, and hexadecimal with zero and x:

>>> 010
8
>>> 0xa
10

You can use hex() and oct() to convert an integer number to an hexadecimal or octal string:

>>> hex(10)
'0xa'

See also

float.hex().

3.2. Promotion

When you mix numeric types in an expression, all operands are converted (or coerced) to the most complex type used in the expression:

>>> 5 + 3.0
8.0

The rules for promotion are

1. if an operand is complex, the other is converted to a complex number
2. otherwise, if an operand is a float, the other is converted to a complex number
3. otherwise, if an operand is a long, the other is converted to a long
4. otherwise, the two operands must be integers.

You can use the coerce() function to check how the promotion will be done:

>>> coerce(1, 2.0)
(1.0, 2.0)

Be careful when divided integers. Indeed, in Python 2.x, the returned value is the quotient. So:

>>> 5/2
2

returns 2, not 2.5 as expected.

3.3. Conversion

Although Python performs conversion internally, you can perform conversion explicitely. Thid can be done with int(), float(), complex(), long() but also oct() and hex().

3.4. Remainder and quotient of a division

The % (modulo) and / signs returns the remainder and quotient of a division:

>>> 5 % 2
1
>>> 5 / 2
2

Alternatively, you can use divmod() function:

>>> divmod(5, 2)
(2, 1)

You can use the % sign fo integer but also float numbers:

>>> 2.2 % 0.7
0.1

3.5. Bit operations

>>> #inverts the bits
>>> ~10
-11
>>> # shift
>>> 8 >> 2
2
>>> # shift
>>> 2 << 2
8
>>> 1&0
0
>>> 1 | 0
1
>>> 1 ^ 1
0

3.6. Raising a number to a power

Just use the ** symbol:

>>> 2**2
4

you can also use th function pow() to raise a power as well.

>>> pow(2,3)
8

You can provide a third argument (mod) so the answer is the remainder of the reuslts divided by the optional argument:

>>> pow(2,3,5)
3

3.7. Augmented assignment operators

The augmented assignment operator are available for the following operator: +, -, *, /, **, %.

>>> x = 1
>>> x += 1
>>> x
2

3.8. More Maths

So far, we’ve seen mathematical operators but no functions. Python provides a few built-in functions to perform more mathematical calculations. Examples are:

abs(), cmp(), max(), min(), round()

Let us quickly present the round function that takes an argument to specify which digit to round:

>>> round(33.49,1)
33.5
>>> round(33.49,-1)
30.0

In addition you can use the math and cmath modules (cmath is the complex version of math). Finally, there is also a random module. See Importing Modules for more details.

3.9. NaN and Inf

>>> float('Inf')
inf
>>> float('Inf')  + 1
inf
>>> float('NaN')
nan
>>> float('NaN') + 1
nan