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#位置参数和关键词参数
#自定义函数，求梯形面积，上底，下底，高。
def trapezoid_area(base_up, base_down, height):
    return 1/2 * (base_up + base_down) * height

#位置参数
print('在函数调用中依次传入参数值的方式称为位置参数')
print('print(trapezoid_area(1,2,3))')
print(trapezoid_area(1,2,3))

#关键词参数
print('在函数调用中传输参数和赋予参数的值的方式称为关键词参数')
print('print(trapezoid_area(base_up=2, base_down=3, height=3))')
print(trapezoid_area(base_up=2, base_down=3, height=3))

#函数中引用参数时可以混合使用位置参数和关键词参数
#仅使用关键词参数时，参数顺序可以打乱
#混合使用参数时，位置参数必须在关键词参数之前

trapezoid_area(height=3, base_down=2, base_up=1) #正确
#trapezoid_area(height=3, base_down=2, 1) #错误
#SyntaxError: positional argument follows keyword argument
#trapezoid_area(base_up=1, base_down=2, 3) #错误
#SyntaxError: positional argument follows keyword argument
trapezoid_area(1, 2, height=3) #正确
trapezoid_area(1, height=3, base_down=2) #正确

PS C:\Users\harveymei> & C:/Users/harveymei/AppData/Local/Programs/Python/Python38/python.exe c:/Users/harveymei/hello.py
在函数调用中依次传入参数值的方式称为位置参数
print(trapezoid_area(1,2,3))
4.5
在函数调用中传输参数和赋予参数的值的方式称为关键词参数
print(trapezoid_area(base_up=2, base_down=3, height=3))
7.5
PS C:\Users\harveymei>

#函数print()与关键字return
def fahrenheit_converter(C):
    fahrenheit = C * 9 / 5 + 32
#    return fahrenheit + 'F'
#禁用自定义函数的return返回，调用print()函数
    print(str(fahrenheit) + 'F')

#开始调用自定义函数
C2F = fahrenheit_converter(35)
print(C2F)
#输出的结果，第一行为指定的print()函数的打印输出
#第二行为调用fahrenheit_converter()函数的输出，函数中无return关键字，所以返回值为空
#Python中的return是可选的

PS C:\Users\harveymei> & C:/Users/harveymei/AppData/Local/Programs/Python/Python38/python.exe c:/Users/harveymei/hello.py
95.0F
None
PS C:\Users\harveymei>

已使用函数的简单总结

print()
print是一个放入对象就能将结果打印的函数
input()
input是一个可以让用户输入信息的函数
len()
len是一个可以测量对象长度的函数
int()
int是一个可以将字符串类型的数字转换成整数类型的函数

Python 3.8内建函数列表

https://docs.python.org/3/library/functions.html

+---------------+-------------+--------------+--------------+----------------+
| abs()         | delattr()   | hash()       | memoryview() | set()          |
+---------------+-------------+--------------+--------------+----------------+
| all()         | dict()      | help()       | min()        | setattr()      |
+---------------+-------------+--------------+--------------+----------------+
| any()         | dir()       | hex()        | next()       | slice()        |
+---------------+-------------+--------------+--------------+----------------+
| ascii()       | divmod()    | id()         | object()     | sorted()       |
+---------------+-------------+--------------+--------------+----------------+
| bin()         | enumerate() | input()      | oct()        | staticmethod() |
+---------------+-------------+--------------+--------------+----------------+
| bool()        | eval()      | int()        | open()       | str()          |
+---------------+-------------+--------------+--------------+----------------+
| breakpoint()  | exec()      | isinstance() | ord()        | sum()          |
+---------------+-------------+--------------+--------------+----------------+
| bytearray()   | filter()    | issubclass() | pow()        | super()        |
+---------------+-------------+--------------+--------------+----------------+
| bytes()       | float()     | iter()       | print()      | tuple()        |
+---------------+-------------+--------------+--------------+----------------+
| callable()    | format()    | len()        | property()   | type()         |
+---------------+-------------+--------------+--------------+----------------+
| chr()         | frozenset() | list()       | range()      | vars()         |
+---------------+-------------+--------------+--------------+----------------+
| classmethod() | getattr()   | locals()     | repr()       | zip()          |
+---------------+-------------+--------------+--------------+----------------+
| compile()     | globals()   | map()        | reversed()   | __import__()   |
+---------------+-------------+--------------+--------------+----------------+
| complex()     | hasattr()   | max()        | round()      |                |
+---------------+-------------+--------------+--------------+----------------+

search = '168'
num_a = '1386-168-0006'
num_b = '1681-222-0006'

print(search + ' is at ' + str(num_a.find(search) + 1) + ' to ' + str(num_a.find(search) + len(search)) + ' of num_a ')
# 168 is at str(num_a.find(search) + 1) to str(num_a.find(search) + len(search)) of num_a
# 168 is at str(5 + 1) to str(5 + 3) of num_a
# 168 is at 6 to 8 of num_a
print(search + ' is at ' + str(num_b.find(search) + 1) + ' to ' + str(num_b.find(search) + len(search)) + ' of num_b ')

PS C:\Users\harveymei> & C:/Users/harveymei/AppData/Local/Programs/Python/Python38/python.exe c:/Users/harveymei/hello.py
168 is at 6 to 8 of num_a 
168 is at 1 to 3 of num_b
PS C:\Users\harveymei>

#找到朋友中的魔鬼
word = 'friends'
find_the_evil_in_your_friends = word[0] + word[2:4] + word[-3:-1]
#f + ie + nd
print(find_the_evil_in_your_friends)

PS C:\Users\harveymei> & C:/Users/harveymei/AppData/Local/Programs/Python/Python38/python.exe c:/Users/harveymei/hello.py
fiend
PS C:\Users\harveymei>