Python菜鸟之路：Python基础-内置函数补充

常用内置函数及用法：

1. callable()

def callable(i_e_, some_kind_of_function): # real signature unknown; restored from __doc__
    """检查对象object是否可调用。如果返回True，object仍然可能调用失败；但如果返回False，调用对象ojbect绝对不会成功
    Return whether the object is callable (i.e., some kind of function).
    
    Note that classes are callable, as are instances of classes with a
    __call__() method.
    """
    pass

案例：

print(callable(0))
out: False

print(callable("mystring"))
out: False

def add(a, b):
    return a + b
print(callable(add))
out: True

class A:
   def method(self):
      return 0
print(callable(A))
out: True

a = A()
print(callable(a))
out: False

class B:
    def __call__(self):
        return 0
print(callable(B))
out: True

b = B()
print(callable(b))
out: True

2. chr()   返回十进制整数对应的ASCII字符。与ord()作用相反

    ord()  ASCII字符转换为对应十进制。与chr()作用相反

def chr(*args, **kwargs): # real signature unknown
    """ Return a Unicode string of one character with ordinal i; 0 <= i <= 0x10ffff. """ 取值范围[0, 255]之间的正数
    pass

def ord(*args, **kwargs): # real signature unknown
    """ Return the Unicode code point for a one-character string. """
    pass

案例：

1 print(chr(97))
2 out: a
3 
4 print(ord('a'))
5 out: 97

3. eval 把字符串当做表达式，执行。有返回值，返回值就是表达式执行的结果

   exec  比eval更牛逼的功能。但是无返回值。只是去执行python代码或者字符串、表达式.如果接收字符串，则编译成python代码并执行。如果接收代码，则执行。

 1 def eval(*args, **kwargs): # real signature unknown
 2     """
 3     Evaluate the given source in the context of globals and locals.
 4     
 5     The source may be a string representing a Python expression
 6     or a code object as returned by compile().
 7     The globals must be a dictionary and locals can be any mapping,
 8     defaulting to the current globals and locals.
 9     If only globals is given, locals defaults to it.
10     """
11     pass
12 
13 def exec(*args, **kwargs): # real signature unknown
14     """
15     Execute the given source in the context of globals and locals.
16     
17     The source may be a string representing one or more Python statements
18     or a code object as returned by compile().
19     The globals must be a dictionary and locals can be any mapping,
20     defaulting to the current globals and locals.
21     If only globals is given, locals defaults to it.
22     """
23     pass

案例：

 1 s = "print(123)"
 2 r = compile(s, "<string>", "exec")
 3 exec(r)
 4 out:123
 5 
 6 s = 'print(123)'
 7 ret = exec(s)
 8 out: 123
 9 print(ret)
10 out: None
11 
12 s = "8*8"
13 ret = eval(s)
14 print(ret)
15 out: 64

4. compile(source, filename, mode[, flags[, dont_inherit]]) 

　　将source编译为代码或者AST对象。代码对象能够通过exec语句来执行或者eval()进行求值。

 1 def compile(*args, **kwargs): # real signature unknown
 2     """
 3     Compile source into a code object that can be executed by exec() or eval().   将source编译为代码或者AST对象。代码对象能够通过exec语句来执行或者eval()进行求值。
 4     
 5     The source code may represent a Python module, statement or expression.
 6     The filename will be used for run-time error messages.
 7     The mode must be 'exec' to compile a module, 'single' to compile a
 8     single (interactive) statement, or 'eval' to compile an expression.
 9     The flags argument, if present, controls which future statements influence
10     the compilation of the code.
11     The dont_inherit argument, if true, stops the compilation inheriting
12     the effects of any future statements in effect in the code calling
13     compile; if absent or false these statements do influence the compilation,
14     in addition to any features explicitly specified.
15     """
16     pass

案例：

1 s = "print(123)"
2 r = compile(s, "<string>", "exec")
3 # 如果不传 <string>参数，就需要传递一个"文件名"参数
4 exec(r)

扩充知识：statement和expression

　　expression是表达式，就是加减乘除等各种运算符号联接起来的式子，statement是语句，如if语句，while，复制语句等。statement里含有expression.

5. random 生成随机数模块，是一个隐藏的random.Random类的实例的random方法。

案例1：生成随机字符串+数字

 1 import random
 2 li = []
 3 for i in range(6):
 4     r = random.randrange(0,5)
 5     if r == 2 or r == 4:
 6         num = random.randrange(0,10)
 7         li.append(str(num))
 8     else:
 9         c = random.randrange(65, 91)
10         li.append(chr(c))
11 print("".join(li))

案例2：生成随机验证码

 1 import random
 2 def generate_verification_code(len=6):
 3     ''' 随机生成6位的验证码 '''
 4     # 注意： 可以生成0-9A-Za-z的列表，也可以指定个list，这里很灵活
 5     # 比如： code_list = ['$','*','.','!','@','~','^','*','<'] # list中可以加特殊字符来增加复杂度
 6     code_list = ['$','*','.','!','@','~','^','*','<'] 
 7     for i in range(10): # 0-9数字
 8         code_list.append(str(i))
 9     for i in range(65, 91): # 对应从“A”到“Z”的ASCII码
10         code_list.append(chr(i))
11     for i in range(97, 123): #对应从“a”到“z”的ASCII码
12         code_list.append(chr(i))
13     myslice = random.sample(code_list, len)  # 从list中随机获取6个元素，作为一个片断返回
14     verification_code = ''.join(myslice) # list to string
15     return verification_code
16 
17 code = generate_verification_code(12)
18 print(code)
19 
20 out: nf1JKl7j<E^t

6. dir() 快速获取模块或者函数提供的功能。返回一个功能列表

   help() 查看对象的功能，可以快速打印源码

 1 def dir(p_object=None): # real signature unknown; restored from __doc__
 2     """
 3     dir([object]) -> list of strings
 4     
 5     If called without an argument, return the names in the current scope.
 6     Else, return an alphabetized list of names comprising (some of) the attributes
 7     of the given object, and of attributes reachable from it.
 8     If the object supplies a method named __dir__, it will be used; otherwise
 9     the default dir() logic is used and returns:
10       for a module object: the module's attributes.
11       for a class object:  its attributes, and recursively the attributes
12         of its bases.
13       for any other object: its attributes, its class's attributes, and
14         recursively the attributes of its class's base classes.
15     """
16     return []

dir.source