实例讲解Python中函数的调用与定义

#!/usr/bin/env python3 
# -*- coding: utf-8 -*- 
 
# 函数调用 
>>> abs(100) 
100 
>>> abs(-110) 
110 
>>> abs(12.34) 
12.34 
>>> abs(1,2) 
Traceback (most recent call last): 
 File "<stdin>",line 1,in <module> 
TypeError: abs() takes exactly one argument (2 given) 
>>> abs('a') 
Traceback (most recent call last): 
 File "<stdin>",in <module> 
TypeError: bad operand type for abs(): 'str' 
>>> max(1,2) 
2 
>>> max(2,3,1,-5) 
3 
>>> int('123') 
123 
>>> int(12.34) 
12 
>>> str(1.23) 
'1.23' 
>>> str(100) 
'100' 
>>> bool(1) 
True 
>>> bool('') 
False 
>>> a = abs # 变量a指向abs函数，相当于引用 
>>> a(-1) # 所以也可以通过a调用abs函数 
1 
 
>>> n1 = 255 
>>> n2 = 1000 
>>> print(hex(n1)) 
0xff 
>>> print(hex(n2)) 
0x3e8 

#!/usr/bin/env python3 
# -*- coding: utf-8 -*- 
 
#函数定义 
def myAbs(x): 
 if x >= 0: 
  return x 
 else: 
  return -x 
 
a = 10 
myAbs(a) 
 
def nop(): # 空函数 
 pass 

if age >= 18: 
 pass 
#缺少了pass，代码就会有语法错误 
>>> if age >= 18: 
... 
 File "<stdin>",line 2 
 
 ^ 
IndentationError: expected an indented block 
 
>>> myAbs(1,in <module> 
TypeError: myAbs() takes 1 positional argument but 2 were given 
>>> myAbs('A') 
Traceback (most recent call last): 
 File "<stdin>",in <module> 
 File "<stdin>",line 2,in myAbs 
TypeError: unorderable types: str() >= int() 
>>> abs('A') 
Traceback (most recent call last): 
 File "<stdin>",in <module> 
TypeError: bad operand type for abs(): 'str' 
 
def myAbs(x): 
 if not isinstance(x,(int,float)): 
  raise TypeError('bad operand type') 
 if x >= 0: 
  return x 
 else: 
  return -x 
 
>>> myAbs('A') 
Traceback (most recent call last): 
 File "<stdin>",line 3,in myAbs 
TypeError: bad operand type 

import math 
def move(x,y,step,angle = 0): 
 nx = x + step * math.cos(angle) 
 ny = y - step * math.sin(angle) 
 return nx,ny 
 
>>> x,y = move(100,100,60,math.pi / 6) 
>>> print(x,y) 
151.96152422706632 70.0 

>>> r = move(100,math.pi / 6) 
>>> print(r) 
(151.96152422706632,70.0) 

import math 
def quadratic(a,b,c): 
 x1 = (-b + math.sqrt(b * b - 4 * a * c)) / (2 * a) 
 x2 = (-b - math.sqrt(b * b - 4 * a * c)) / (2 * a) 
 return x1,x2 
 
x1,x2 = quadratic(2,5,1) 
print(x1,x2) 
 
>>> import math 
>>> def quadratic(a,c): 
...  x1 = (-b + math.sqrt(b * b - 4 * a * c)) / (2 * a) 
...  x2 = (-b - math.sqrt(b * b - 4 * a * c)) / (2 * a) 
...  return x1,x2 
... 
>>> x1,1) 
>>> print(x1,x2) 
-0.21922359359558485 -2.2807764064044154