py-函数基础

定义: 函数是指将一组语句的集合通过一个名字(函数名)封装起来，要想执行这个函数，只需调用其函数名即可

特性:

1.减少重复代码2.使程序变的可扩展3.使程序变得易维护

函数参数

形参变量

只有在被调用时才分配内存单元，在调用结束时，即刻释放所分配的内存单元。因此，形参只在函数内部有效。函数调用结束返回主调用函数后则不能再使用该形参变量

实参可以是常量、变量、表达式、函数等，无论实参是何种类型的量，在进行函数调用时，它们都必须有确定的值，以便把这些值传送给形参。因此应预先用赋值，输入等办法使参数获得确定值

def calc(x,y): # x,y 是形参，用来接受参数 res = x*y return rest = calc(2,3) # 2,3 是实参，实际传入的参数， print(t)

默认参数

def staff(name,age,skill,year=2018): #默认参数一般放到实参后面print('staff info'.center(20,'-'))print("name:",name)print("age:",age)print("skill:",skill)print("year:",year) staff("lemi",22,"python_devops")

关键参数正常情况下，给函数传参数要按顺序，不想按顺序就可以用关键参数，只需指定参数名即可(指定了参数名的参数就叫关键参数)，但记住一个要求就是，关键参数必须放在位置参数(以位置顺序确定对应关系的参数)之后

def staff(name,age,skill,year=2018): print('staff info'.center(20,'-')) print("name:",name) print("age:",age) print("skill:",skill) print("year:",year)staff("lemi",skill="python_devops",22) # 不可以 staff("kevin",skill="linux",age=22) #可以这样 staff("walk",25,"linux",age=22) #不可以，相当于两次赋值 # 总结：不想按位置参数，一一对应的去传值， # 就使用关键参数(参数名=值)，但得只能在位置参数后面， # 相当于，你不想排队一个个进，想按名进去， # 那你就只能等到前面排队的进完再进，不然混乱(报错)

非固定参数

若你的函数在定义时不确定用户想传入多少个参数，就可以使用非固定参数# *args 会把多传入的参数变成一个元组形式(args也可以其他形式命名，相当于形参)# args,如果没传值,就为空 ()

def staff(name,age,*args): print(name,age,args) staff('lemi',22,'python','CQ') # 输出 # lemi 22 ('python', 'CQ')

当*args在其他形参前面时会截胡，传递参数时，他后面的参数用关键参数可以解决def staff(name,*args,age): passstaff(‘lemi’,’python’,’linux’,age=22)staff(‘lemi’,*[‘python’,’linux’],age=22) 解包，传给形参args

# *kwargs 会把多传入的参数(key-value型)变成一个dict形式{}# kwargs,如果没传值,就为空 {}

def staff(name,age,*args,**kwargs): print(name,age,args,kwargs) staff('lemi',22,'linux','web',skill='python',place='CQ') # 输出 #lemi 22 ('linux', 'web') {'skill': 'python', 'place': 'CQ'}staff('lemi',22,'linux','web',**{’skill’:'python',’place’:'CQ'}) 效果跟上面一样

返回值

函数外部的代码要想获取函数的执行结果，就可以在函数里用return语句把结果返回

def staff(name,age,skill,year=2018): print('staff info'.center(20,'-'))print("name:",name)print("age:",age)print("skill:",skill)print("year:",year)if age>22:return Falseelse:return True interview = staff("lemi",22,"python_devops") if interview:print(interview)print('面试成功') else:print('have to improve')output: -----staff info----- name: lemi age: 22 skill: python_devops year: 2018 面试成功 True View Code

注意

函数在执行过程中只要遇到return语句，就会停止执行并返回结果，也可以理解为 return 语句代表着函数的结束如果未在函数中指定return,那这个函数的返回值为None函数,只能返回一个值

全局与局部变量

status = 'poor man' def work(status):print('before learn python:',status)status = 'Charming male'print('after change:',status)work(status)print('看看外面status改变了吗？',status)output: before learn python: poor man after change: Charming male 看看status改变了吗？ poor man不用传name 值到函数里，也可以在函数里调用外面的变量 # 局部函数可以调用全局变量，但是不能修改 status = 'poor man' def work():status = 'Charming male'print('after change:',status) work() print('看看外面status改变了吗？',status) output: after change: Charming male 看看外面status改变了吗？ poor man View Code

1.在函数中定义的变量称为局部变量，在程序的一开始定义的变量称为全局变量。2.全局变量作用域是整个程序，局部变量作用域是定义该变量的函数。3.当全局变量与局部变量同名时，在定义局部变量的函数内，局部变量起作用；在其它地方全局变量起作用。

修改全局变量

status = 'poor man' def work(): global status status = 'Charming male' print('after change:',status) work() print('看看外面status改变了吗？',status) output after change: Charming male 看看外面status改变了吗？ Charming male View Code

global status的作用就是要在函数里声明status是全局变量,最上面的status='poor man'即使不写，程序最后面的print也可以打印status

变量是列表时， 当修改的是列表时，可以删除元素，修改元素skill = ['linux','python','html'] def change_skill():skill = ['linux','python']print(skill) #此处不能修改 change_skill() print(skill)['linux', 'python'] ['linux', 'python', 'html']------------------skill = ['linux','python','html'] def change_skill():skill[2] = 'hadoop'skill.remove('linux')print('inside',skill) #这里可以该，改的是元素，并不是列表对象#因为在内存里，列表对象整体是一个地址，元素又是另一个地址 change_skill() print('outside',skill)inside ['python', 'hadoop'] outside ['python', 'hadoop'] View Code

作用域

作用域(scope)，程序设计概念，通常来说，一段程序代码中所用到的名字并不总是有效/可用的，而限定这个名字的可用性的代码范围就是这个名字的作用域。python中函数就是一个作用域，局部变量放置在其作用域中。代码定义完，作用域已经生成，无论在任何地方调用，作用域链向上查找

age = 21 def func1():age = 22def func2():print(age)return func2 val = func1() print(val) val()output <function func1.<locals>.func2 at 0x000002AB58965BF8> 22 View Code

嵌套函数

name = 'bird kevin' def work():name = 'common staff'def work_1():name = 'outstanding staff'print('level 3',name)work_1()print('level 2',name) work() print('level now',name)OUTPUT level 3 outstanding staff level 2 common staff level now bird kevin # 最外层不能调用work_1()里层函数#小游戏 age = 19 def func1():global agedef func2():print(age)age = 73func2() func1() print(age) #output>>> 73 73age = 19 def func1():def func2():print(age)func2()age = 73func1() print(age) #会报错，不知道找哪一个 View Code

 

匿名函数

匿名函数就是不需要显式的指定函数名

#a = lambda x,y:x*y print(a(1,2)) lambda 不能有复杂的逻辑。可以三元运算res = map(lambda x:x**2,[1,5,7,4,8]) for i in res: print(i) 输出1 25 49 16 64 节省代码

高阶函数

变量可以指向函数，函数的参数能接收变量，那么一个函数就可以接收另一个函数作为参数，这种函数就称之为高阶函数。

def add(x,y,f):return f(x) + f(y) res = add(3,-6,abs) print(res)

只需满足以下任意一个条件，即是高阶函数

1.接受一个或多个函数作为输入

2.return 返回另外一个函数

递归

在函数内部，可以调用其他函数。如果一个函数在内部调用自身本身，这个函数就是递归函数

def fac(n):if n == 1:return 1else:return n *fac(n-1) print(fac(3))def calc(n):v = int(n/2)print(v)if v > 0:calc(v)print(n)calc(10)output5 2 1 0 1 2 5 10先一层层进去，再往外走 View Code

递归特性:

1.必须有一个明确的结束条件

2.每次进入更深一层递归时，问题规模相比上次递归都应有所减少

3.递归效率不高，递归层次过多会导致栈溢出(在计算机中，函数调用是通过栈(stack)这种数据结构实现的，每当进入一个函数调用，栈就会加一层栈帧，每当函数返回，栈就会减一层栈帧。由于栈的大小不是无限的，所以，递归调用的次数过多，会导致栈溢出)

堆栈扫盲

尾递归，调用下一层的时候就退出了 def cal(n):print(n)return cal(n+1) cal(1) 在python并没有优化 View Code

内置函数

内置参数详解

>>> min([2,3,4]) #返回数字序列最小值2 >>> max([2,3,4]) # 返回数字序列最大值4>>> help(all) Help on built-in function all in module builtins: all(iterable, /)Return True if bool(x) is True for all values x in the iterable.If the iterable is empty, return True.>>> a = [1,2,3] >>> all(a) True >>> a.append(0) >>> all(a) False >>> a.append([]) >>> all(a) False >>> all([]) True>>>help(any) Help on built-in function any in module builtins:any(iterable, /)Return True if bool(x) is True for any x in the iterable.If the iterable is empty, return False.dir 打印当前下变量>>> help(hex)Help on built-in function hex in module builtins:hex(number, /)Return the hexadecimal representation of an integer.>>> hex(12648430)'0xc0ffee'>>> 10//3 3 >>> divmod(10,3) (3, 1) >>> sorted([22,31,13,3,14,1,34,3]) [1, 3, 3, 13, 14, 22, 31, 34] >>> d = {} >>> for i in range(20):d[i] = i-2>>> d {0: -2, 1: -1, 2: 0, 3: 1, 4: 2, 5: 3, 6: 4, 7: 5, 8: 6, 9: 7, 10: 8, 11: 9, 12: 10, 13: 11, 14: 12, 15: 13, 16: 14, 17: 15, 18: 16, 19: 17} >>> sorted(d) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19] >>> d.items <built-in method items of dict object at 0x0000023C083AF5E8> >>> d.items() dict_items([(0, -2), (1, -1), (2, 0), (3, 1), (4, 2), (5, 3), (6, 4), (7, 5), (8, 6), (9, 7), (10, 8), (11, 9), (12, 10), (13, 11), (14, 12), (15, 13), (16, 14), (17, 15), (18, 16), (19, 17)]) >>> sorted(d.items(),key) Traceback (most recent call last):File "<pyshell#11>", line 1, in <module>sorted(d.items(),key) NameError: name 'key' is not defined >>> sorted(d.items(),key=lambda x:x[1]) [(0, -2), (1, -1), (2, 0), (3, 1), (4, 2), (5, 3), (6, 4), (7, 5), (8, 6), (9, 7), (10, 8), (11, 9), (12, 10), (13, 11), (14, 12), (15, 13), (16, 14), (17, 15), (18, 16), (19, 17)] >>> sorted(d.items(),key=lambda x:x[1],reverse = True) [(19, 17), (18, 16), (17, 15), (16, 14), (15, 13), (14, 12), (13, 11), (12, 10), (11, 9), (10, 8), (9, 7), (8, 6), (7, 5), (6, 4), (5, 3), (4, 2), (3, 1), (2, 0), (1, -1), (0, -2)] >>> ascii('n') "'n'" >>> ascii('你') "'\\u4f60'" >>> oct(10) '0o12' >>> bin(10) '0b1010' >>> help(eval) Help on built-in function eval in module builtins:eval(source, globals=None, locals=None, /)Evaluate the given source in the context of globals and locals.The source may be a string representing a Python expressionor a code object as returned by compile().The globals must be a dictionary and locals can be any mapping,defaulting to the current globals and locals.If only globals is given, locals defaults to it.>>> eval('1+7') 8 >>> eval('print('hello world')') SyntaxError: invalid syntax >>> eval('print("hello world")') hello world >>> code = ''' if 5 > 4:print('ok') else:print('fail')''' >>> eval(code) Traceback (most recent call last):File "<pyshell#27>", line 1, in <module>eval(code)File "<string>", line 2if 5 > 4:^ SyntaxError: invalid syntax >>> 只能处理简单单行代码 Traceback (most recent call last):File "<pyshell#28>", line 1, in <module>只能处理简单单行代码 NameError: name '只能处理简单单行代码' is not defined >>> exec(code) ok >>> help(exec) Help on built-in function exec in module builtins:exec(source, globals=None, locals=None, /)Execute the given source in the context of globals and locals.The source may be a string representing one or more Python statementsor a code object as returned by compile().The globals must be a dictionary and locals can be any mapping,defaulting to the current globals and locals.If only globals is given, locals defaults to it.>>> res = eval('1+3+4') >>> res1 = exec('1+3+4') >>> print('res',res,res1) res 8 None >>> exec可以执行多行但拿不到返回值 KeyboardInterrupt >>> eval执行单行可以拿到返回值 KeyboardInterrupt >>> ord('a') 97 >>> chr('98') Traceback (most recent call last):File "<pyshell#35>", line 1, in <module>chr('98') TypeError: an integer is required (got type str) >>> chr(98) 'b' >>> s = '元贞' >>> s[0] '元' >>> s.encode('utf-8') b'\xe5\x85\x83\xe8\xb4\x9e' >>> s1 = bytearray(s) Traceback (most recent call last):File "<pyshell#40>", line 1, in <module>s1 = bytearray(s) TypeError: string argument without an encoding >>> s1 = bytearray(s.encode (utf-8)) Traceback (most recent call last):File "<pyshell#41>", line 1, in <module>s1 = bytearray(s.encode (utf-8)) NameError: name 'utf' is not defined >>> s1 = bytearray(s.encode ('utf-8')) >>> s1[0] = 'a' Traceback (most recent call last):File "<pyshell#43>", line 1, in <module>s1[0] = 'a' TypeError: an integer is required >>> s1[0] = 65 >>> s '元贞' >>> s1 bytearray(b'A\x85\x83\xe8\xb4\x9e') >>> s1[4] 180 >>> id(s[0]) 2456860022384 >>> 源地址修改 KeyboardInterrupt >>> map(lambda x:x*x,[1,2,3]) <map object at 0x0000023C0842C908> >>> list(map(lambda x:x*x,[1,2,3])) [1, 4, 9] >>> list(map(lambda x:x<3,[1,2,3])) [True, True, False] >>> list(filter(lambda x:x<3,[1,2,3])) [1, 2] >>> import functools >>> functools.reduce <built-in function reduce> >>> bytes('34') Traceback (most recent call last):File "<pyshell#55>", line 1, in <module>bytes('34') TypeError: string argument without an encoding >>> bytes('34)SyntaxError: EOL while scanning string literal >>> bytes(34)b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' >>> bytes('你好')Traceback (most recent call last):File "<pyshell#58>", line 1, in <module>bytes('你好') TypeError: string argument without an encoding >>> bytes(你好)Traceback (most recent call last):File "<pyshell#59>", line 1, in <module>bytes(你好) NameError: name '你好' is not defined >>> print('python','linux',sep='->')python->linux >>> print('python','linux',end='->')python linux-> >>> print('python','linux')python linux >>> print('python','linux',end='')python linux >>>msg = 'linux is lady ' f = open('skill.txt','w') print(msg,'python is yong woman',sep='|',end="",file=f) print(msg,'python is yong woman',sep='|',end="",file=f)>>> def f():pass>>> a = [1,2,3]>>> callable(f)True >>> callable(a)False>>> s = {1,2,3,4}>>> s.discard(2)>>> s{1, 3, 4} >>> s = frozenset(s)>>> sfrozenset({1, 3, 4}) >>> >>> >>> s.discard(3)Traceback (most recent call last):File "<pyshell#77>", line 1, in <module>s.discard(3) AttributeError: 'frozenset' object has no attribute 'discard' >>> s.remove(2)Traceback (most recent call last):File "<pyshell#78>", line 1, in <module>s.remove(2) AttributeError: 'frozenset' object has no attribute 'remove'打印变量名和对应的值 >>> vars(){'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'd': {0: -2, 1: -1, 2: 0, 3: 1, 4: 2, 5: 3, 6: 4, 7: 5, 8: 6, 9: 7, 10: 8, 11: 9, 12: 10, 13: 11, 14: 12, 15: 13, 16: 14, 17: 15, 18: 16, 19: 17}, 'i': 19, 'code': "\nif 5 > 4:\n print('ok')\nelse:\n print('fail')", 'res': 8, 'res1': None, 's': frozenset({1, 3, 4}), 's1': bytearray(b'A\x85\x83\xe8\xb4\x9e'), 'functools': <module 'functools' from 'C:\\Users\\Administrator\\AppData\\Local\\Programs\\Python\\Python36\\lib\\functools.py'>, 'f': <function f at 0x0000023C08464400>, 'a': [1, 2, 3]}>>> def f():n = 3print(locals())>>> f(){'n': 3} >>> globals(){'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'd': {0: -2, 1: -1, 2: 0, 3: 1, 4: 2, 5: 3, 6: 4, 7: 5, 8: 6, 9: 7, 10: 8, 11: 9, 12: 10, 13: 11, 14: 12, 15: 13, 16: 14, 17: 15, 18: 16, 19: 17}, 'i': 19, 'code': "\nif 5 > 4:\n print('ok')\nelse:\n print('fail')", 'res': 8, 'res1': None, 's': frozenset({1, 3, 4}), 's1': bytearray(b'A\x85\x83\xe8\xb4\x9e'), 'functools': <module 'functools' from 'C:\\Users\\Administrator\\AppData\\Local\\Programs\\Python\\Python36\\lib\\functools.py'>, 'f': <function f at 0x0000023C084646A8>, 'a': [1, 2, 3]} >>>>>> a[1, 2, 3] >>> repr(a)'[1, 2, 3]'>>> a[1, 2, 3] >>> b = [6,7,8]>>> zip(a,b)()Traceback (most recent call last):File "<pyshell#96>", line 1, in <module>zip(a,b)() TypeError: 'zip' object is not callable >>> list(zip(a,b))[(1, 6), (2, 7), (3, 8)] >>> View Code

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