python内置函数与匿名函数

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

input用法

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
     """

print源码剖析

 f = open('tmp_file','w')
 print(,,sep=',',file = f,flush=True)

file关键字说明

 from time import sleep
 for i in range(,,):
     sleep(0.1)
     str="*"*(i//2)
     print('\r%s%%:%s'%(i,str),end="",flush=True)

打印进度条

数据类型相关

type(s)返回s的数据类型

s="abc"
print(type(s))#<class 'str'>

type说明

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=[,,]
 l2=(,,)
 print(hash(l2))#
 print(hash(l1))#TypeError: unhashable type: 'list'

hash举例

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('.'))

__import__

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=) -> str
  |
  |      Return a copy of S where all tab characters are expanded using spaces.
  |      If tabsize is not given, a tab size of  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 - 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 - 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=-) -> 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=-) -> 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.

help用法

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())#Flase

callable实例

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']

dir实例

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')

bytearray

 ret = memoryview(bytes('你好',encoding='utf-8'))
 print(len(ret))
 print(bytes(ret[:]).decode('utf-8'))
 print(bytes(ret[:]).decode('utf-8'))

memoryview

序列：reversed，slice

 l=[,,,,,]
 l.reverse()
 print(l)#[, , , , , ]

reverse

 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]

slice

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]

filter

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]

map

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)])

Code

 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。

习题