Python Functions and modules

Introduction

In Python there is also the concept of functions, the standard function we can call built-in functions, such functions can be directly called through the function name. But there are other functions that are not built-in that cannot be called directly from the function name, such as the floor function (rounding down), and we need to use the module; This article mainly introduces math and Cmath.

Python version: 3.4.4

Built-in functions (standard functions)

Let's take a look at the standard function, and if you test with the idle program, the color of the function name will turn purple when you enter the built-in function, not the built-in function.

1.abs: Absolute Value

>>> ABS (-5)5

2.pow (x, y): x y-square

>>> Pow (2,3)8

Non-built-in functions

Grammar

Import Math[cmath]math[cmath].function_name

Or

From Math[cmath] Improt function_name

Note: The usage of Cmath is the same as math, but Cmath is used to deal with complex numbers, such as when you need to square root a negative number, you need to use Cmath

1.floor: Rounding Down

>>> Floor (31.5) Traceback (recent):  "<pyshell#70>  "1 in <module> floor    (31.5' )  Floor '  is not defined

Because floor is not a standard function, the direct call will error, then need to use the module.

>>> Import Math>>> Math.floor (31.5)

 from Math Importfloor >>> floor (31.5)

2.sqrt: Take square root

>>> Import Math>>> math.sqrt (4)2.0>>> math.sqrt (- 4 ) Traceback (most recent)  :"<pyshell#82>"1  in <module>    math.sqrt (-4) Valueerror:math domain error

You can see that using math to take the square root of negative numbers will be an error, then you need to use Cmath

>>> Import Cmath>>> cmath.sqrt (-4) 2j

 from cmath import sqrt>>> sqrt (-4) 2j

Other functions

Summary

The syntax of Python changes in every new version and requires constant attention to where each new version has changed.

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Python Functions and modules