Python菜鸟之路一：Python基础-内置函数补充
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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 []
案例：
1 print(dir(dict)) 2 3 out: [\'__class__\', \'__contains__\', \'__delattr__\', \'__delitem__\', \'__dir__\', \'__doc__\', \'__eq__\', \'__format__\', \'__ge__\', \'__getattribute__\', \'__getitem__\', \'__gt__\', \'__hash__\', \'__init__\', \'__iter__\', \'__le__\', \'__len__\', \'__lt__\', \'__ne__\', \'__new__\', \'__reduce__\', \'__reduce_ex__\', \'__repr__\', \'__setattr__\', \'__setitem__\', \'__sizeof__\', \'__str__\', \'__subclasshook__\', \'clear\', \'copy\', \'fromkeys\', \'get\', \'items\', \'keys\', \'pop\', \'popitem\', \'setdefault\', \'update\', \'values\']
1 print(help(dict)) 2 3 out: Help on class dict in module builtins: 4 5 class dict(object) 6 | dict() -> new empty dictionary 7 | dict(mapping) -> new dictionary initialized from a mapping object\'s 8 | (key, value) pairs 9 | dict(iterable) -> new dictionary initialized as if via: 10 | d = {} 11 | for k, v in iterable: 12 | d[k] = v 13 | dict(**kwargs) -> new dictionary initialized with the name=value pairs 14 | in the keyword argument list. For example: dict(one=1, two=2) 15 | 16 | Methods defined here: 17 | 18 | __contains__(self, key, /) 19 | True if D has a key k, else False. 20 | 21 | __delitem__(self, key, /) 22 | Delete self[key]. 23 | 24 | __eq__(self, value, /) 25 | Return self==value. 26 | 27 | __ge__(self, value, /) 28 | Return self>=value. 29 | 30 | __getattribute__(self, name, /) 31 | Return getattr(self, name). 32 | 33 | __getitem__(...) 34 | x.__getitem__(y) <==> x[y] 35 | 36 | __gt__(self, value, /) 37 | Return self>value. 38 | 39 | __init__(self, /, *args, **kwargs) 40 | Initialize self. See help(type(self)) for accurate signature. 41 | 42 | __iter__(self, /) 43 | Implement iter(self). 44 | 45 | __le__(self, value, /) 46 | Return self<=value. 47 | 48 | __len__(self, /) 49 | Return len(self). 50 | 51 | __lt__(self, value, /) 52 | Return self<value. 53 | 54 | __ne__(self, value, /) 55 | Return self!=value. 56 | 57 | __new__(*args, **kwargs) from builtins.type 58 | Create and return a new object. See help(type) for accurate signature. 59 | 60 | __repr__(self, /) 61 | Return repr(self). 62 | 63 | __setitem__(self, key, value, /) 64 | Set self[key] to value. 65 | 66 | __sizeof__(...) 67 | D.__sizeof__() -> size of D in memory, in bytes 68 | 69 | clear(...) 70 | D.clear() -> None. Remove all items from D. 71 | 72 | copy(...) 73 | D.copy() -> a shallow copy of D 74 | 75 | fromkeys(iterable, value=None, /) from builtins.type 76 | Returns a new dict with keys from iterable and values equal to value. 77 | 78 | get(...) 79 | D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None. 80 | 81 | items(...) 82 | D.items() -> a set-like object providing a view on D\'s items 83 | 84 | keys(...) 85 | D.keys() -> a set-like object providing a view on D\'s keys 86 | 87 | pop(...) 88 | D.pop(k[,d]) -> v, remove specified key and return the corresponding value. 89 | If key is not found, d is returned if given, otherwise KeyError is raised 90 | 91 | popitem(...) 92 | D.popitem() -> (k, v), remove and return some (key, value) pair as a 93 | 2-tuple; but raise KeyError if D is empty. 94 | 95 | setdefault(...) 96 | D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D 97 | 98 | update(...) 99 | D.update([E, ]**F) -> None. Update D from dict/iterable E and F. 100 | If E is present and has a .keys() method, then does: for k in E: D[k] = E[k] 101 | If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v 102 | In either case, this is followed by: for k in F: D[k] = F[k] 103 | 104 | values(...) 105 | D.values() -> an object providing a view on D\'s values 106 | 107 | ---------------------------------------------------------------------- 108 | Data and other attributes defined here: 109 | 110 | __hash__ = None 111 112 None
7. divmod(x, y) 得到x/y的商和余数 (商, 余数)
1 print(divmod(5,4)) 2 3 out： (1, 1)
8. isinstance() 判断对象是谁的实例, 可以向上查找，甚至查找父类的父类。返回True or False
1 print(isinstance(\'a\', str)) 2 3 out: True
9. globals() 代表所有的全局变量，返回的 dictionary 的任何的改动都会直接影响到全局变量。
locals() 代表所有的局部变量,返回 dictionary 的函数, 并且在 dictionary 中设置一个值。是一个只读dict
1 def foo(arg, a): 2 x = 1 3 y = \'xxxxxx\' 4 for i in range(10): 5 j = 1 6 k = i 7 print locals() 8 9 10 #调用函数的打印结果 11 foo(1,2) 12 out: {\'a\': 2, \'i\': 9, \'k\': 9, \'j\': 1, \'arg\': 1, \'y\': \'xxxxxx\', \'x\': 1}
10. len 返回对象的长度，python2中按照字节计算 ， python3按照字符来计算
1 print(len("诸葛亮")) 2 3 #python2 4 out: 9 5 #python3 6 out: 3
11. hash 返回对象的哈希值
1 print(hash("abc")) 2 3 out: -8810164989165849038
12. filter 把传入的函数依次作用于每个元素，然后根据返回值是True还是False决定保留还是丢弃该元素。
1 class filter(object): 2 """ 3 filter(function or None, iterable) --> filter object 4 5 Return an iterator yielding those items of iterable for which function(item) 6 is true. If function is None, return the items that are true. 7 """ 8 def __getattribute__(self, *args, **kwargs): # real signature unknown 9 """ Return getattr(self, name). """ 10 pass 11 12 def __init__(self, function_or_None, iterable): # real signature unknown; restored from __doc__ 13 pass 14 15 def __iter__(self, *args, **kwargs): # real signature unknown 16 """ Implement iter(self). """ 17 pass 18 19 @staticmethod # known case of __new__ 20 def __new__(*args, **kwargs): # real signature unknown 21 """ Create and return a new object. See help(type) for accurate signature. """ 22 pass 23 24 def __next__(self, *args, **kwargs): # real signature unknown 25 """ Implement next(self). """ 26 pass 27 28 def __reduce__(self, *args, **kwargs): # real signature unknown 29 """ Return state information for pickling. """ 30 pass
案例：
1 def is_odd(n): 2 return n % 2 == 1 3 4 print(list(filter(is_odd, [1, 2, 4, 5, 6, 9, 10, 15]))) 5 6 out: [1, 5, 9, 15]
13. map 将传入的函数依次作用到序列的每个元素，并把结果作为新的Iterator返回
1 class map(object): 2 """ 3 map(func, *iterables) --> map object 4 5 Make an iterator that computes the function using arguments from 6 each of the iterables. Stops when the shortest iterable is exhausted. 将迭代对象按照func的方法进行运算逐个，最终返回一个list对象 7 """ 8 def __getattribute__(self, *args, **kwargs): # real signature unknown 9 """ Return getattr(self, name). """ 10 pass 11 12 def __init__(self, func, *iterables): # real signature unknown; restored from __doc__ 13 pass 14 15 def __iter__(self, *args, **kwargs): # real signature unknown 16 """ Implement iter(self). """ 17 pass 18 19 @staticmethod # known case of __new__ 20 def __new__(*args, **kwargs): # real signature unknown 21 """ Create and return a new object. See help(type) for accurate signature. """ 22 pass 23 24 def __next__(self, *args, **k以上是关于Python菜鸟之路一：Python基础-内置函数补充的主要内容，如果未能解决你的问题，请参考以下文章