python成长之路——第四天
内置函数:
生成一个6位的随机验证码:
callable:查看对象是否能被调用(对象是函数的话能被调用)
#callable def f1(): pass f2="a" print(callable(f1)) print(callable(f2))
#chr() 将ascii码转换成对应的字符
#ord() 相反
print(chr(65)) print(ord("B"))
#!/usr/bin/env python # -*- coding:utf-8 -*- import random li=[] for i in range(6): r=random.randrange(0,5) if r == 2: temp=random.randrange(0,10) li.append(str(temp)) #注意:join方法要求列表里的每个元素必须是字符串 elif r == 4: temp=random.randrange(97,123) k=chr(temp) li.append(k) else: temp=random.randrange(65,91) k=chr(temp) li.append(k) print("".join(li))
V67Dj2A
compile() 将字符串,编译成python代码
exec() 执行 比eval功能更强大,直接执行python代码或者字符串(如果接收的是字符串的话,内部会执行compile),没有返回值
eval() 执行 主要是用来执行表达式的,有返回值
python解释器执行文件要经过以下几个步骤:
1.读取文件内容到内存 open—str到内存open完成
2.python解释器把 字符串—》编译—》特殊代码 compile完成
3.执行代码exec完成
编译模式:
single:编译成单行的python程序
eval:编译成表达式
exec:编译成和python代码一模一样的东西
with open("zy.py","r",encoding="utf8") as f: r = compile(f.read(),"<string>","exec") exec(r)
BBDfji
zy.py是上面的6位随机验证码程序,这个就模拟了python解释器的执行过程
s = "print(123)" r = compile(s,"<string>","exec") print(r) print(type(r)) exec(r)
<code object <module> at 0x0000000000802DB0, file "<string>", line 1>
<class 'code'>
123
s = ''' print(123) print(456) ''' r = compile(s,"<string>","single") exec(r)
Traceback (most recent call last):
File "C:/Users/Administrator/PycharmProjects/untitled/day4.py", line 14, in <module>
r = compile(s,"<string>","single")
File "<string>", line 2
print(123)
^
SyntaxError: multiple statements found while compiling a single statement
s = ''' print(123) print(456) ''' r = compile(s,"<string>","exec") exec(r)
123
456
print(eval("2+3")) a="[1,2,3,4]" li=eval(a) print(type(li)) b='{"k1":"v1","k2":"v2"}' dic=eval(b) print(type(dic))
5
<class 'list'>
<class 'dict'>
delattr,getattr,setattr,hasattr 反射 以后讲
dir() 快速查看一个对象提供什么功能,不显示功能详细
help() 显示功能详细
divmod()
#divmod() 得到商和余数,返回值是元组 #共97 每页显示10 总共多少页 print(divmod(97,10)) n1, n2 = divmod(97,10) print("n1",n1) print("n2",n2)
(9, 7)
n1 9
n2 7
对象是类的实例 则True
isinstance()
#isinstance() 判断对象是否是某个类的实例 s="alex" r=isinstance(s,list) print(r)
False
filter(函数,可迭代的对象)
def f1(a): if a>22: return True li=[11,22,33,44,55] ret = filter(f1,li) print(ret) print(list(ret))
<filter object at 0x0000000001142198>
[33, 44, 55]
filter和lambda组合:
li=[11,22,33,44,55] ret = filter(lambda a: a > 33,li) print(list(ret))
[44, 55]
map(函数,可迭代对象),对可迭代对象的每个元素都进行处理
li=[11,22,33,44,55] def f(a): return a+100 ret = map(f,li) print(ret) print(list(ret))
<map object at 0x0000000000B82128>
[111, 122, 133, 144, 155]
li=[11,22,33,44,55] ret = map(lambda a: a+100 , li) print(ret) print(list(ret))
<map object at 0x00000000011C2128>
[111, 122, 133, 144, 155]
filter:函数返回True 则元素添加到结果中
map: 将函数返回值添加到结果中
NAME = "alex" def show(): a=123 print(globals()) print(locals()) show()
{'__package__': None, '__loader__': <_frozen_importlib_external.SourceFileLoader object at 0x0000000000A05BA8>, '__builtins__': <module 'builtins' (built-in)>, 'show': <function show at 0x0000000001169C80>, '__cached__': None, '__name__': '__main__', '__doc__': None, '__spec__': None, '__file__': 'C:/Users/Administrator/PycharmProjects/untitled/day4.py', 'NAME': 'alex'}
{'a': 123}
如果一个字符串是字典或者列表等形式的,一定是单引号在外边,双引号在里面
装饰器:
@ + 函数名
功能:
1.自动执行outer函数并且将其下面的函数名f1当作参数传递
2.将outer函数的返回值,重复赋值给f1
详细过程:
1. 将outer函数加载入内存
2. 执行@outer 将函数名f1传给func(func=原f1),执行outer
3. 将inner函数加载入内存
4. 将outer函数的返回值inner,重新赋值给f1,(f1=inner)
5. 当调用f1时,就执行inner(),inner中的func=原f1
适用场景:
主要是权限控制
def outer(func): def inner(*args,**kwargs): print("before") ret = func(*args,**kwargs) print("after") return ret return inner @outer def f1(aa): print("F1") return aa @outer def f2(*args,**kwargs): print("F2") for index,items in enumerate(args): print(index,"-"*5,items) for k in kwargs: print(k,"-"*5,kwargs[k]) f2(1,2,3,a=1,b=2,c=3)
before
F2
0 ----- 1
1 ----- 2
2 ----- 3
b ----- 2
c ----- 3
a ----- 1
after