基于python内置函数与匿名函数详解
内置函数
Built-in Functions | ||||
---|---|---|---|---|
abs() | dict() | help() | min() | setattr() |
all() | dir() | hex() | next() | slice() |
any() | divmod() | id() | object() | sorted() |
ascii() | enumerate() | input() | oct() | staticmethod() |
bin() | eval() | int() | open() | str() |
bool() | exec() | isinstance() | 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() | |
bytearray() | filter() | issubclass() | pow() | super() |
delattr() | hash() | memoryview() | set |
截止到python版本3.6.2,现在python一共为我们提供了68个内置函数。它们就是python提供给你直接可以拿来使用的所有函数。
内置函数分类
作用域相关
基于字典的形式获取局部变量和全局变量
globals()——获取全局变量的字典
locals()——获取执行本方法所在命名空间内的局部变量的字典
其他
输入输出相关
input()输入
s = input("请输入内容 : ") #输入的内容赋值给s变量 print(s) #输入什么打印什么。数据类型是str
print输出
def print(self, *args, sep=' ', end='\n', file=None): # known special case of print """ print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False) file: 默认是输出到屏幕,如果设置为文件句柄,输出到文件 sep: 打印多个值之间的分隔符,默认为空格 end: 每一次打印的结尾,默认为换行符 flush: 立即把内容输出到流文件,不作缓存 """
f = open('tmp_file','w') print(123,456,sep=',',file = f,flush=True)
from time import sleep for i in range(0,101,2): sleep(0.1) str="*"*(i//2) print('\r%s%%:%s'%(i,str),end="",flush=True)
数据类型相关
type(s)返回s的数据类型
s="abc" print(type(s))#<class 'str'>
内存相关
id(s) s是参数,返回一个变量的内存地址
hash(s) s是参数,返回一个可hash变量的哈希值,不可hash的变量被hash之后会报错。
l1=[1,2,3] l2=(1,2,3) print(hash(l2))#2528502973977326415 print(hash(l1))#TypeError: unhashable type: 'list'
hash函数会根据一个内部的算法对当前可hash变量进行处理,返回一个int数字。
*每一次执行程序,内容相同的变量hash值在这一次执行过程中不会发生改变。
hash函数会根据一个内部的算法对当前可hash变量进行处理,返回一个int数字。
*每一次执行程序,内容相同的变量hash值在这一次执行过程中不会发生改变。
文件操作相关
open() 打开一个文件,返回一个文件操作符(文件句柄)
操作文件的模式有r,w,a,r+,w+,a+ 共6种,每一种方式都可以用二进制的形式操作(rb,wb,ab,rb+,wb+,ab+)
可以用encoding指定编码.
模块操作相关
__import__导入一个模块
os = __import__('os') print(os.path.abspath('.'))
帮助方法
help(s) s为函数名
help(str) #输出 class str(object) | str(object='') -> str | str(bytes_or_buffer[, encoding[, errors]]) -> str | | Create a new string object from the given object. If encoding or | errors is specified, then the object must expose a data buffer | that will be decoded using the given encoding and error handler. | Otherwise, returns the result of object.__str__() (if defined) | or repr(object). | encoding defaults to sys.getdefaultencoding(). | errors defaults to 'strict'. | | Methods defined here: | | __add__(self, value, /) | Return self+value. | | __contains__(self, key, /) | Return key in self. | | __eq__(self, value, /) | Return self==value. | | __format__(...) | S.__format__(format_spec) -> str | | Return a formatted version of S as described by format_spec. | | __ge__(self, value, /) | Return self>=value. | | __getattribute__(self, name, /) | Return getattr(self, name). | | __getitem__(self, key, /) | Return self[key]. | | __getnewargs__(...) | | __gt__(self, value, /) | Return self>value. | | __hash__(self, /) | Return hash(self). | | __iter__(self, /) | Implement iter(self). | | __le__(self, value, /) | Return self<=value. | | __len__(self, /) | Return len(self). | | __lt__(self, value, /) | Return self<value. | | __mod__(self, value, /) | Return self%value. | | __mul__(self, value, /) | Return self*value.n | | __ne__(self, value, /) | Return self!=value. | | __new__(*args, **kwargs) from builtins.type | Create and return a new object. See help(type) for accurate signature. | | __repr__(self, /) | Return repr(self). | | __rmod__(self, value, /) | Return value%self. | | __rmul__(self, value, /) | Return self*value. | | __sizeof__(...) | S.__sizeof__() -> size of S in memory, in bytes | | __str__(self, /) | Return str(self). | | capitalize(...) | S.capitalize() -> str | | Return a capitalized version of S, i.e. make the first character | have upper case and the rest lower case. | | casefold(...) | S.casefold() -> str | | Return a version of S suitable for caseless comparisons. | | center(...) | S.center(width[, fillchar]) -> str | | Return S centered in a string of length width. Padding is | done using the specified fill character (default is a space) | | count(...) | S.count(sub[, start[, end]]) -> int | | Return the number of non-overlapping occurrences of substring sub in | string S[start:end]. Optional arguments start and end are | interpreted as in slice notation. | | encode(...) | S.encode(encoding='utf-8', errors='strict') -> bytes | | Encode S using the codec registered for encoding. Default encoding | is 'utf-8'. errors may be given to set a different error | handling scheme. Default is 'strict' meaning that encoding errors raise | a UnicodeEncodeError. Other possible values are 'ignore', 'replace' and | 'xmlcharrefreplace' as well as any other name registered with | codecs.register_error that can handle UnicodeEncodeErrors. | | endswith(...) | S.endswith(suffix[, start[, end]]) -> bool | | Return True if S ends with the specified suffix, False otherwise. | With optional start, test S beginning at that position. | With optional end, stop comparing S at that position. | suffix can also be a tuple of strings to try. | | expandtabs(...) | S.expandtabs(tabsize=8) -> str | | Return a copy of S where all tab characters are expanded using spaces. | If tabsize is not given, a tab size of 8 characters is assumed. | | find(...) | S.find(sub[, start[, end]]) -> int | | Return the lowest index in S where substring sub is found, | such that sub is contained within S[start:end]. Optional | arguments start and end are interpreted as in slice notation. | | Return -1 on failure. | | format(...) | S.format(*args, **kwargs) -> str | | Return a formatted version of S, using substitutions from args and kwargs. | The substitutions are identified by braces ('{' and '}'). | | format_map(...) | S.format_map(mapping) -> str | | Return a formatted version of S, using substitutions from mapping. | The substitutions are identified by braces ('{' and '}'). | | index(...) | S.index(sub[, start[, end]]) -> int | | Return the lowest index in S where substring sub is found, | such that sub is contained within S[start:end]. Optional | arguments start and end are interpreted as in slice notation. | | Raises ValueError when the substring is not found. | | isalnum(...) | S.isalnum() -> bool | | Return True if all characters in S are alphanumeric | and there is at least one character in S, False otherwise. | | isalpha(...) | S.isalpha() -> bool | | Return True if all characters in S are alphabetic | and there is at least one character in S, False otherwise. | | isdecimal(...) | S.isdecimal() -> bool | | Return True if there are only decimal characters in S, | False otherwise. | | isdigit(...) | S.isdigit() -> bool | | Return True if all characters in S are digits | and there is at least one character in S, False otherwise. | | isidentifier(...) | S.isidentifier() -> bool | | Return True if S is a valid identifier according | to the language definition. | | Use keyword.iskeyword() to test for reserved identifiers | such as "def" and "class". | | islower(...) | S.islower() -> bool | | Return True if all cased characters in S are lowercase and there is | at least one cased character in S, False otherwise. | | isnumeric(...) | S.isnumeric() -> bool | | Return True if there are only numeric characters in S, | False otherwise. | | isprintable(...) | S.isprintable() -> bool | | Return True if all characters in S are considered | printable in repr() or S is empty, False otherwise. | | isspace(...) | S.isspace() -> bool | | Return True if all characters in S are whitespace | and there is at least one character in S, False otherwise. | | istitle(...) | S.istitle() -> bool | | Return True if S is a titlecased string and there is at least one | character in S, i.e. upper- and titlecase characters may only | follow uncased characters and lowercase characters only cased ones. | Return False otherwise. | | isupper(...) | S.isupper() -> bool | | Return True if all cased characters in S are uppercase and there is | at least one cased character in S, False otherwise. | | join(...) | S.join(iterable) -> str | | Return a string which is the concatenation of the strings in the | iterable. The separator between elements is S. | | ljust(...) | S.ljust(width[, fillchar]) -> str | | Return S left-justified in a Unicode string of length width. Padding is | done using the specified fill character (default is a space). | | lower(...) | S.lower() -> str | | Return a copy of the string S converted to lowercase. | | lstrip(...) | S.lstrip([chars]) -> str | | Return a copy of the string S with leading whitespace removed. | If chars is given and not None, remove characters in chars instead. | | partition(...) | S.partition(sep) -> (head, sep, tail) | | Search for the separator sep in S, and return the part before it, | the separator itself, and the part after it. If the separator is not | found, return S and two empty strings. | | replace(...) | S.replace(old, new[, count]) -> str | | Return a copy of S with all occurrences of substring | old replaced by new. If the optional argument count is | given, only the first count occurrences are replaced. | | rfind(...) | S.rfind(sub[, start[, end]]) -> int | | Return the highest index in S where substring sub is found, | such that sub is contained within S[start:end]. Optional | arguments start and end are interpreted as in slice notation. | | Return -1 on failure. | | rindex(...) | S.rindex(sub[, start[, end]]) -> int | | Return the highest index in S where substring sub is found, | such that sub is contained within S[start:end]. Optional | arguments start and end are interpreted as in slice notation. | | Raises ValueError when the substring is not found. | | rjust(...) | S.rjust(width[, fillchar]) -> str | | Return S right-justified in a string of length width. Padding is | done using the specified fill character (default is a space). | | rpartition(...) | S.rpartition(sep) -> (head, sep, tail) | | Search for the separator sep in S, starting at the end of S, and return | the part before it, the separator itself, and the part after it. If the | separator is not found, return two empty strings and S. | | rsplit(...) | S.rsplit(sep=None, maxsplit=-1) -> list of strings | | Return a list of the words in S, using sep as the | delimiter string, starting at the end of the string and | working to the front. If maxsplit is given, at most maxsplit | splits are done. If sep is not specified, any whitespace string | is a separator. | | rstrip(...) | S.rstrip([chars]) -> str | | Return a copy of the string S with trailing whitespace removed. | If chars is given and not None, remove characters in chars instead. | | split(...) | S.split(sep=None, maxsplit=-1) -> list of strings | | Return a list of the words in S, using sep as the | delimiter string. If maxsplit is given, at most maxsplit | splits are done. If sep is not specified or is None, any | whitespace string is a separator and empty strings are | removed from the result. | | splitlines(...) | S.splitlines([keepends]) -> list of strings | | Return a list of the lines in S, breaking at line boundaries. | Line breaks are not included in the resulting list unless keepends | is given and true. | | startswith(...) | S.startswith(prefix[, start[, end]]) -> bool | | Return True if S starts with the specified prefix, False otherwise. | With optional start, test S beginning at that position. | With optional end, stop comparing S at that position. | prefix can also be a tuple of strings to try. | | strip(...) | S.strip([chars]) -> str | | Return a copy of the string S with leading and trailing | whitespace removed. | If chars is given and not None, remove characters in chars instead. | | swapcase(...) | S.swapcase() -> str | | Return a copy of S with uppercase characters converted to lowercase | and vice versa. | | title(...) | S.title() -> str | | Return a titlecased version of S, i.e. words start with title case | characters, all remaining cased characters have lower case. | | translate(...) | S.translate(table) -> str | | Return a copy of the string S in which each character has been mapped | through the given translation table. The table must implement | lookup/indexing via __getitem__, for instance a dictionary or list, | mapping Unicode ordinals to Unicode ordinals, strings, or None. If | this operation raises LookupError, the character is left untouched. | Characters mapped to None are deleted. | | upper(...) | S.upper() -> str | | Return a copy of S converted to uppercase. | | zfill(...) | S.zfill(width) -> str | | Pad a numeric string S with zeros on the left, to fill a field | of the specified width. The string S is never truncated. | | ---------------------------------------------------------------------- | Static methods defined here: | | maketrans(x, y=None, z=None, /) | Return a translation table usable for str.translate(). | | If there is only one argument, it must be a dictionary mapping Unicode | ordinals (integers) or characters to Unicode ordinals, strings or None. | Character keys will be then converted to ordinals. | If there are two arguments, they must be strings of equal length, and | in the resulting dictionary, each character in x will be mapped to the | character at the same position in y. If there is a third argument, it | must be a string, whose characters will be mapped to None in the result.
在控制台执行help()进入帮助模式。可以随意输入变量或者变量的类型。输入q退出
或者直接执行help(o),o是参数,查看和变量o有关的操作。。。
和调用相关
callable(s),s是参数,看这个变量是不是可调用。
如果s是一个函数名,就会返回True
def func():pass print(callable(func))#True print(callable(123))#Flase
查看参数所属类型的所有内置方法
dir() 默认查看全局空间内的属性,也接受一个参数,查看这个参数内的方法或变量
dir(list) ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
和数字相关
数字——数据类型相关:bool,int,float,complex
数字——进制转换相关:bin,oct,hex
数字——数学运算:abs,divmod,min,max,sum,round,pow
和数据结构相关
序列——列表和元组相关的:list和tuple
序列——字符串相关的:str,format,bytes,bytearry,memoryview,ord,chr,ascii,repr
ret=bytearray('xiaozhangmen',encoding='utf-8') print(ret)#bytearray(b'xiaozhangmen')
ret = memoryview(bytes('你好',encoding='utf-8')) print(len(ret)) print(bytes(ret[:3]).decode('utf-8')) print(bytes(ret[3:]).decode('utf-8'))
序列:reversed,slice
l=[1,2,3,4,5,6] l.reverse() print(l)#[6, 5, 4, 3, 2, 1]
l=[1,2,3,4,5,6] sli=slice(1,4,2)#slice看起来返回的是一个规则,拿到这个规则后再对列表进行操作 print(l[sli])#[2, 4]
数据集合——字典和集合:dict,set,frozenset
数据集合:len,sorted,enumerate,all,any,zip,filter,map
filter:使用指定方法过滤可迭代对象的元素
def is_odd(x): return x % 2 == 1 print(filter(is_odd,[1,2,3,4,5,6]))#<filter object at 0x00000000022EC240> print(list(filter(is_odd,[1,2,3,4,5,6])))#[1, 3, 5]
map:python中的map函数应用于每一个可迭代的项,返回的是一个结果list。如果有其他的可迭代参数传进来,map函数则会把每一个参数都以相应的处理函数进行迭代处理。map()函数接收两个参数,一个是函数,一个是序列,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list返回。
def pow(x): return x**2 print(map(pow,[0,1,2,3]))#<map object at 0x000000000291C1D0> print(list(map(pow,[0,1,2,3])))#[0, 1, 4, 9]
匿名函数
匿名函数:为了解决那些功能很简单的需求而设计的一句话函数
匿名函数格式:
函数名 = lambda 参数 :返回值 #参数可以有多个,用逗号隔开 #匿名函数不管逻辑多复杂,只能写一行,且逻辑执行结束后的内容就是返回值 #返回值和正常的函数一样可以是任意数据类型
匿名函数实例
#如把下面函数改为匿名函数 def add(x,y): return x+y add1=lambda x,y:x+y print(add(1,2)) print(add1(1,2))
面试题笔记:
现有两个元组(('a'),('b')),(('c'),('d')),请使用python中匿名函数生成列表[{'a':'c'},{'b':'d'}]
#答案一 test = lambda t1,t2 :[{i:j} for i,j in zip(t1,t2)] print(test(t1,t2)) #答案二 print(list(map(lambda t:{t[0]:t[1]},zip(t1,t2)))) #还可以这样写 print([{i:j} for i,j in zip(t1,t2)])
1.下面程序的输出结果是: d = lambda p:p*2 t = lambda p:p*3 x = 2 x = d(x) x = t(x) x = d(x) print x 2.现有两元组(('a'),('b')),(('c'),('d')),请使用python中匿名函数生成列表[{'a':'c'},{'b':'d'}] 3.以下代码的输出是什么?请给出答案并解释。 def multipliers(): return [lambda x:i*x for i in range(4)] print([m(2) for m in multipliers()]) 请修改multipliers的定义来产生期望的结果。
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