Python Learning note __2.2 defining functions

# This is a learning note for the Liaoche teacher Python tutorial

1. Defining functions

defining a function requires a function name, a parameter, and a function body . In the function body, it is better to pass the parameter judgment.

1.1. Function creation

Define a function with Def, data type check with Isinstance. Examples are as follows:

def my_abs (x):

if not isinstance (x, (int, float)): # Determine the parameters passed in, whether it is xxx or floating-point

raise TypeError (' bad operand type ') # throws an error

If x >= 0:

return x

Else

Return-x

1.2. Empty function creation

If you want to define an empty function that doesn't do anything, you can use the PASS statement

Def NOP ():

Pass

The pass statement does nothing. When you're not sure how to write code, use it as a placeholder

1.3. Import of functions

You can import functions from a well-written. py script with import, or you can import the system's own modules to use the functions in the module

Importing system Modules

Import Math

After importing the Math module, we can use the MATH.SQRT () function

Import from A. py script (file name does not write suffix)

Form Test Import quadratic

From the test file, import the quadratic function

1.4. function returns multiple values

Defining functions

Import Math

def move (x, y, step, angle=0):

NX = x + step * Math.Cos (angle)

NY = y-step * Math.sin (angle)

Return NX, NY

Call

>>>x, y = Move (+, +, MATH.PI/6)

>>>print (x, y)

151.96152422706632 70.0

Explain

>>>r = Move (+, +, MATH.PI/6)

>>>print (R)

(151.96152422706632, 70.0)

Returning multiple function values is actually a tuple, which, in syntax, returns a tuple that can omit parentheses

1.5. Summary

When defining functions, it is necessary to determine the number of function names and parameters;

If necessary, the data type of the parameter can be checked first;

The function body can return the function result at any time with return;

Automatically return none when the function has finished executing and there is no return statement.

A function can return multiple values at the same time, but is actually a tuple.

2. Example

Defines a function quadratic (a, B, c), receives 3 parameters, returns a unary two-second equation:

AX2 + bx + c = 0 of two solutions.

Tip: Calculating the square root can call the Math.sqrt () function:

#!/usr/bin/env Python3

#-*-Coding:utf-8-*-

Import Math

def quadratic (a,b,c):

n = b*b-4*a*c # b*b = = b**2. Can be analogy b**3,b**4 .....

If n<0:

Print (' No real solution ')

Elif n==0:

x=-b/(2*a)

return x

Else

x1= (-B + math.sqrt (n))/(2*a)

X2= (-B-MATH.SQRT (n))/(2*a)

Return x1,x2

Python Learning note __2.2 defining functions