匿名函数
例子
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返回两个数的和
def add(x, y): return x + y # 等价于 add = lambda x, y: x + y -
返回字典中值最大的key
dic = {'a': 13, 'b': 3, 'c': 34} print(max(dic,key=lambda x:dic[x]))
面试题
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题1
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'}]
ret = zip((('a'),('b')),(('c'),('d'))) res = map(lambda tup:{tup[0]:tup[1]},ret) print(list(res)) -
题2
写出下列代码输出结果
def multipliers(): return [lambda x: i * x for i in range(4)] # 返回3个匿名函数,到执行时i的值已为3 print([m(2) for m in multipliers()]) # result: # [6, 6, 6, 6]
内置函数
数字相关
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数据类型转换
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bool()
转布尔类型
print(bool([])) # False print(bool('')) # False print(bool(0)) # False print(bool({})) # False print(bool(())) # False -
int()
转整形
- float()
转浮点型
')) # 3.0
- complex()
转复数类型
')) # (3+0j)
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进制转换
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bin()
转二进制
print(bin(2)) # 0b10
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oct()
转八进制
print(oct(2)) # 0o2
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hex()
转十六进制
print(hex(2)) # 0x2
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数学运算
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abs()
绝对值
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divmod()
除余
print(divmod(9, 4)) # (2, 1) 商2余1
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round()
精确小数位
print(round(3.5687789,3)) # 3.569
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pow()
幂运算
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sum()
求和
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max()
最大值
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min()
最小值
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数据结构相关
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类型转换
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list()
转列表类型
print(list((1,2,3))) # [1, 2, 3]
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tuple()
转元组类型
print(tuple([1,2,3])) # (1, 2, 3)
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dict()
转字典类型
print(dict({1:'a',2:'b'})) # {1: 'a', 2: 'b'} -
set()
转集合类型
print(set([1,1,2,3,3])) # {1, 2, 3} -
frozenset()
转不可变集合类型
only_read_set = frozenset([1, 1, 2, 3, 3]); print(only_read_set) # frozenset({1, 2, 3}) only_read_set[1] = 4 # TypeError: 'frozenset' object does not support item assignment
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字符串相关
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str()
转字符串
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format()
1.将一个数值进行格式化显示
2.如果参数format_spec未提供,则和调用str()效果相同
3.对于不同的类型,参数format_spec可提供的值都不一样
print(format(3.1415926)) # 3.1415926 # 字符串:指定对齐方式，<是左对齐， >是右对齐，^是居中对齐 print(format('format', '<20')) print(format('format', '>20')) print(format('format', '^20')) # result: # format # format # format # 整形: # 转换成二进制 # 转换unicode成字符 print(format(97, 'c')) # a # 转换成10进制 # 转换成8进制 # 转换成16进制 小写字母表示 print(format(11, 'x')) # b # 转换成16进制 大写字母表示 print(format(11, 'X')) # B # 和d一样 # 默认和d一样 # 浮点型: # 科学计数法，默认保留6位小数 print(format(314159267, 'e')) # '3.141593e+08' # 科学计数法，指定保留2位小数 print(format(314159267, '0.2e')) # '3.14e+08' # 科学计数法，指定保留2位小数，采用大写E表示 print(format(314159267, '0.2E')) # '3.14E+08' # 小数点计数法，默认保留6位小数 print(format(314159267, 'f')) # '314159267.000000' # 小数点计数法，默认保留6位小数 print(format(3.14159267000, 'f')) # '3.141593' ##小数点计数法，指定保留8位小数 print(format(3.14159267000, '0.8f')) # '3.14159267' # 小数点计数法，指定保留10位小数 print(format(3.14159267000, '0.10f')) # '3.1415926700' # 小数点计数法，无穷大转换成大小字母 print(format(3.14e+1000000, 'F')) # 'INF' -
bytes()
转字节
print(bytes('aaa', 'utf8')) # b'aaa' print('aaa'.encode('utf8')) # b'aaa' -
bytearray()
转字节数组
print(bytearray('aaa', 'utf8')) # bytearray(b'aaa') for i in bytearray('aaa', 'utf8'): print(i) -
memoryview()
查看bytes内存地址
print(memoryview(bytes('a', 'utf8'))) # <memory at 0x000000000272A588> -
ord()
字符按unicode转数字
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chr()
数字按unicode转字符
print(chr(97)) # 'a'
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ascii()
转ascii码
# 只要是ascii码中的内容,就原样输出,不是就转换成\u格式 print(ascii('张三')) # '\u5f20\u4e09' -
repr()
将一个对象以字符串形式返回
print('hello%r' % 'world') # hello'world' ')) # '1' print(repr([1, 2, 3])) # [1, 2, 3]
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相关内置函数
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len()
返回可迭代对象长度
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enumerate()
枚举化
print(list(enumerate(['a', 'b', 'c']))) # [(0, 'a'), (1, 'b'), (2, 'c')]
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all()
所有值都为True则返回True,否则返回False
print(all([True, '', 1])) # False
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any()
存在一个值为True则返回True,否则返回False
print(any([True, False, 0, ''])) # True
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zip()
拉链方法,返回一个迭代器
num_list = [1, 2, 3] letter_list = ['a', 'b', 'c'] print(zip(num_list, letter_list)) # <zip object at 0x00000000021DB648> print(list(zip(num_list, letter_list))) # [(1, 'a'), (2, 'b'), (3, 'c')]
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filter()
过滤
# 筛选num_list里的奇数 num_list = [1, 2, 3, 4, 5, 6] result_list = filter(lambda i: i % 2 == 1, num_list) print(list(result_list)) # [1, 3, 5] # 等价于 print(list(i for i in num_list if i % 2 == 1)) # [1, 3, 5]
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map()
映射
# 取列表中每个数的平方 num_list = [1, 2, 3, 4, 5, 6] print(list(map(lambda i: i ** 2, num_list))) # [1, 4, 9, 16, 25, 36]
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sorted()
排序
num_list = [-1, -2, 3, -4] # 默认排序 print(sorted(num_list)) # [-4, -2, -1, 3] # 以列表中数字的绝对值升序 print(sorted(num_list, key=abs)) # [-1, -2, 3, -4] # 以列表中数字的绝对值降序 print(sorted(num_list, key=abs, reverse=True)) # [-4, 3, -2, -1]
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面向对象相关
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定义特殊方法的装饰器
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classmethod
定义类方法
class A: @classmethod def print(self): print('from A') A.print() # from A -
classmethod
定义静态方法
class A: @staticmethod def print(): print('from A') A.print() # from A -
property
将方法包装成属性
class Person: def __init__(self, name, age): self.__name = name self.__age = age @property def name(self): return self.__name @name.setter def name(self, new_name): self.__name = new_name @name.deleter def name(self): print('执行删除name操作') p = Person('张三', 18) print(p.name) # 张三 p.name = '李四' print(p.name) # 李四 # 只是触发对应deleter装饰的函数,具体操作需在函数类完成 del p.name # 执行删除name操作 print(p.name) # 李四
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判断对象/类与类之间的关系
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isinstance()
判断一个对象是不是指定类的实例
class A: pass class B: pass a = A() print(isinstance(a, A)) # True print(isinstance(a, B)) # False
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issubclass()
判断一个类指定类的子类
class A: pass class B(A): pass class C: pass print(issubclass(B, A)) # True print(issubclass(B, C)) # False
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object()
所有类的基类
class A: pass class B(A): pass class C: pass print(issubclass(A, object)) # True print(issubclass(B, object)) # True print(issubclass(C, object)) # True
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super()
获取父类
class A: @classmethod def func(self): print('print in A') class B(A): @classmethod def func(self): super().func() super(B, self).func() print('print in B') B.func() # result: # print in A # print in A # print in B
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其它
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作用域相关
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locals()
将当前函数块的所有变量以字典类型返回
a = 1 def outer(): a = 2 def inner(): b = 3 print(locals()) inner() outer() # result # {'b': 3} -
globals()
将全局变量以字典类型返回
a = 1 def outer(): a = 2 def inner(): b = 3 print(globals()) inner() outer() # result # {'__name__': '__main__', '__doc__': None, '__package__': None, ..., 'a': 1, 'outer': <function outer at 0x000000000203C268>}
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迭代器/生成器相关
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range()
返回指定区间数字生成器
for i in range(1, 4): print(i) # result: -
iter()
传入可迭代对象返回迭代器
print(iter(range(1, 4))) # <range_iterator object at 0x0000000002792470>
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next()
迭代器取下一个值
range_iter = iter(range(1, 3)) print(range_iter.__next__()) # StopIteration 取不到值抛异常
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字符串类型代码的执行
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eval()
执行且有返回值
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exec()
执行无返回值
print(exec('1+1')) # None -
compile()
返回字符串编译后字节代码对象
str = "for i in range(0,10): print(i)" c = compile(str, '', 'exec') # 编译为字节代码对象 exec(c) # result: str = "3 * 4 + 5" a = compile(str, '', 'eval')
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反射相关
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hasattr()
判断指定类或实例是否拥有指定属性
class Person: gender = '男' def __init__(self, name, age): self.name = name self.age = age # 判断Person的实例p是否拥有name属性 p = Person('张三', '李四') print(hasattr(p, 'name')) # True # 判断Person类是否拥有name属性 print(hasattr(Person, 'name')) # False # 判断Person类是否拥有gender属性 print(hasattr(Person, 'gender')) # True -
getattr()
获取指定类或实例的指定属性引用
class Person: gender = '男' def __init__(self, name, age): self.name = name self.age = age def show_name(self): print(self.name) p = Person('张三', 18) # 获取实例的属性 print(getattr(p, 'age')) # 获取实例的方法 getattr(p, 'show_name')() -
setattr()
给指定类或对象的属性赋值,没有则创建后再赋值
class Person: def __init__(self, name, age): self.name = name self.age = age def show_name(self): print(self.name) print(hasattr(Person, 'gender')) # False 默认没有gender属性 setattr(Person, 'gender', '男') print(hasattr(Person, 'gender')) # True -
delattr()
删除指定类或对象的指定属性
class Person: gender = '男' def __init__(self, name, age): self.name = name self.age = age def show_name(self): print(self.name) print(hasattr(Person, 'gender')) # True delattr(Person, 'gender') print(hasattr(Person, 'gender')) # False
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输入输出
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input()
以字符串类型返回输入值
>>> input('input your name:') input your name:zhangsan 'zhangsan' -
print()
输出
>>> print('hello world') hello world
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内存相关
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hash()
返回对象在内存中的哈希标识
print(hash('a')) # -1985915095439783199 -
id()
返回对象在内存中的地址标识
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文件操作相关
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open()
具体见文件操作
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模块相关
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__import__()
模块导入
time =__import__('time')# 等价于 import time print(time.time())
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调用相关
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callable()
判断对象是否可调用,返回True或False
def func(): return 1 + 1 a = 1 print(callable(a)) # False a = func print(callable(a)) # True
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查看信息
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help()
返回类型的帮助信息
print(help(str)) # result: # 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__(self, format_spec, /) # | Return a formatted version of the string 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. # | # | __ne__(self, value, /) # | Return self!=value. # | # | __repr__(self, /) # | Return repr(self). # | # | __rmod__(self, value, /) # | Return value%self. # | # | __rmul__(self, value, /) # | Return value*self. # | # | __sizeof__(self, /) # | Return the size of the string in memory, in bytes. # | # | __str__(self, /) # | Return str(self). # | # | capitalize(self, /) # | Return a capitalized version of the string. # | # | More specifically, make the first character have upper case and the rest lower # | case. # | # | casefold(self, /) # | Return a version of the string suitable for caseless comparisons. # | # | center(self, width, fillchar=' ', /) # | Return a centered 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(self, /, encoding='utf-8', errors='strict') # | Encode the string using the codec registered for encoding. # | # | encoding # | The encoding in which to encode the string. # | errors # | The error handling scheme to use for encoding errors. # | The 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(self, /, tabsize=8) # | Return a copy 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(self, /) # | Return True if the string is an alpha-numeric string, False otherwise. # | # | A string is alpha-numeric if all characters in the string are alpha-numeric and # | there is at least one character in the string. # | # | isalpha(self, /) # | Return True if the string is an alphabetic string, False otherwise. # | # | A string is alphabetic if all characters in the string are alphabetic and there # | is at least one character in the string. # | # | isascii(self, /) # | Return True if all characters in the string are ASCII, False otherwise. # | # | ASCII characters have code points in the range U+0000-U+007F. # | Empty string is ASCII too. # | # | isdecimal(self, /) # | Return True if the string is a decimal string, False otherwise. # | # | A string is a decimal string if all characters in the string are decimal and # | there is at least one character in the string. # | # | isdigit(self, /) # | Return True if the string is a digit string, False otherwise. # | # | A string is a digit string if all characters in the string are digits and there # | is at least one character in the string. # | # | isidentifier(self, /) # | Return True if the string is a valid Python identifier, False otherwise. # | # | Use keyword.iskeyword() to test for reserved identifiers such as "def" and # | "class". # | # | islower(self, /) # | Return True if the string is a lowercase string, False otherwise. # | # | A string is lowercase if all cased characters in the string are lowercase and # | there is at least one cased character in the string. # | # | isnumeric(self, /) # | Return True if the string is a numeric string, False otherwise. # | # | A string is numeric if all characters in the string are numeric and there is at # | least one character in the string. # | # | isprintable(self, /) # | Return True if the string is printable, False otherwise. # | # | A string is printable if all of its characters are considered printable in # | repr() or if it is empty. # | # | isspace(self, /) # | Return True if the string is a whitespace string, False otherwise. # | # | A string is whitespace if all characters in the string are whitespace and there # | is at least one character in the string. # | # | istitle(self, /) # | Return True if the string is a title-cased string, False otherwise. # | # | In a title-cased string, upper- and title-case characters may only # | follow uncased characters and lowercase characters only cased ones. # | # | isupper(self, /) # | Return True if the string is an uppercase string, False otherwise. # | # | A string is uppercase if all cased characters in the string are uppercase and # | there is at least one cased character in the string. # | # | join(self, iterable, /) # | Concatenate any number of strings. # | # | The string whose method is called is inserted in between each given string. # | The result is returned as a new string. # | # | Example: '.'.join(['ab', 'pq', 'rs']) -> 'ab.pq.rs' # | # | ljust(self, width, fillchar=' ', /) # | Return a left-justified string of length width. # | # | Padding is done using the specified fill character (default is a space). # | # | lower(self, /) # | Return a copy of the string converted to lowercase. # | # | lstrip(self, chars=None, /) # | Return a copy of the string with leading whitespace removed. # | # | If chars is given and not None, remove characters in chars instead. # | # | partition(self, sep, /) # | Partition the string into three parts using the given separator. # | # | This will search for the separator in the string. If the separator is found, # | returns a 3-tuple containing the part before the separator, the separator # | itself, and the part after it. # | # | If the separator is not found, returns a 3-tuple containing the original string # | and two empty strings. # | # | replace(self, old, new, count=-1, /) # | Return a copy with all occurrences of substring old replaced by new. # | # | count # | Maximum number of occurrences to replace. # | -1 (the default value) means replace all occurrences. # | # | 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(self, width, fillchar=' ', /) # | Return a right-justified string of length width. # | # | Padding is done using the specified fill character (default is a space). # | # | rpartition(self, sep, /) # | Partition the string into three parts using the given separator. # | # | This will search for the separator in the string, starting at the end. If # | the separator is found, returns a 3-tuple containing the part before the # | separator, the separator itself, and the part after it. # | # | If the separator is not found, returns a 3-tuple containing two empty strings # | and the original string. # | # | rsplit(self, /, sep=None, maxsplit=-1) # | Return a list of the words in the string, using sep as the delimiter string. # | # | sep # | The delimiter according which to split the string. # | None (the default value) means split according to any whitespace, # | and discard empty strings from the result. # | maxsplit # | Maximum number of splits to do. # | -1 (the default value) means no limit. # | # | Splits are done starting at the end of the string and working to the front. # | # | rstrip(self, chars=None, /) # | Return a copy of the string with trailing whitespace removed. # | # | If chars is given and not None, remove characters in chars instead. # | # | split(self, /, sep=None, maxsplit=-1) # | Return a list of the words in the string, using sep as the delimiter string. # | # | sep # | The delimiter according which to split the string. # | None (the default value) means split according to any whitespace, # | and discard empty strings from the result. # | maxsplit # | Maximum number of splits to do. # | -1 (the default value) means no limit. # | # | splitlines(self, /, keepends=False) # | Return a list of the lines in the string, 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(self, chars=None, /) # | Return a copy of the string with leading and trailing whitespace remove. # | # | If chars is given and not None, remove characters in chars instead. # | # | swapcase(self, /) # | Convert uppercase characters to lowercase and lowercase characters to uppercase. # | # | title(self, /) # | Return a version of the string where each word is titlecased. # | # | More specifically, words start with uppercased characters and all remaining # | cased characters have lower case. # | # | translate(self, table, /) # | Replace each character in the string using the given translation table. # | # | table # | Translation table, which must be a mapping of Unicode ordinals to # | Unicode ordinals, strings, or None. # | # | The table must implement lookup/indexing via __getitem__, for instance a # | dictionary or list. If this operation raises LookupError, the character is # | left untouched. Characters mapped to None are deleted. # | # | upper(self, /) # | Return a copy of the string converted to uppercase. # | # | zfill(self, width, /) # | Pad a numeric string with zeros on the left, to fill a field of the given width. # | # | The string is never truncated. # | # | ---------------------------------------------------------------------- # | Static methods defined here: # | # | __new__(*args, **kwargs) from builtins.type # | Create and return a new object. See help(type) for accurate signature. # | # | 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. # # None # -
dir()
以字符串列表返回对象类型的属性及函数
print(dir( 'a')) # ['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
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