目录
一、字符串
1、字符串的定义
1-1、使用单引号(')
1-2、使用双引号(")
1-3、使用三引号('''或""")
1-4、原始字符串(r'str'或R'str')
2、字符串的语法
3、获取字符串的属性和方法
4、获取字符串的帮助信息
5、字符串的用法
5-1、capitalize()方法
5-2、casefold()方法
5-3、center()方法
5-4、count()方法
5-5、encode()方法
5-6、endswith()方法
5-7、expandtabs()方法
5-8、find()方法
5-9、format()方法
5-10、format_map()方法
5-11、index()方法
5-12、isalnum()方法
5-13、isalpha()方法
5-14、isascii()方法
5-15、isdigit()方法
二、推荐阅读
1、Python-VBA函数之旅-str()函数
2、Python算法之旅
3、Python函数之旅
4、个人主页-神奇夜光杯-CSDN
一、字符串
1、字符串的定义
在Python中，字符串(Str)是一种数据类型，用于存储一系列字符(文本)，字符串可以包含字母、数字、标点符号和特殊字符等。
在Python中，可以通过以下几种方式定义字符串：
1-1、使用单引号(')
s1 = 'Hello, my Python World!'
print(type(s1)) # 输出：<class 'str'>1-2、使用双引号(")
s1 = "Hello, my Python World!"
print(type(s1)) # 输出：<class 'str'>1-3、使用三引号('''或""")
# 使用三个单引号：'''
s1 = '''Hello, my Python World!'''
print(type(s1)) # 输出：<class 'str'>
# 使用三个双引号："""
s1 = """Hello, my Python World!"""
print(type(s1)) # 输出：<class 'str'>1-4、原始字符串(r'str'或R'str')
# 用r'str'
path1 = r'C:\Users\Username\Documents\file.txt'
print(type(path1)) # 输出：<class 'str'>
# 用r"str"
path2 = r"C:\Users\Username\Documents\file.txt"
print(type(path2)) # 输出：<class 'str'>
# 用r'''str'''
path3 = r'''C:\Users\Username\Documents\file.txt'''
print(type(path3)) # 输出：<class 'str'>
# 用r"""str"""
path4 = r"""C:\Users\Username\Documents\file.txt"""
print(type(path4)) # 输出：<class 'str'>
# 用R'str'
path5 = R'C:\Users\Username\Documents\file.txt'
print(type(path5)) # 输出：<class 'str'>
# 用R"str"
path6 = R"C:\Users\Username\Documents\file.txt"
print(type(path6)) # 输出：<class 'str'>
# 用R'''str'''
path7 = R'''C:\Users\Username\Documents\file.txt'''
print(type(path7)) # 输出：<class 'str'>
# 用R"""str"""
path8 = R"""C:\Users\Username\Documents\file.txt"""
print(type(path8)) # 输出：<class 'str'>2、字符串的语法
Python中的字符串是由单引号(')、双引号(")或三引号(''' 或 """)括起来的字符或文本，字符串可以是ASCII字符、Unicode字符或两者都有。
3、获取字符串的属性和方法
用dir()函数获取str所有属性和方法的列表
print(dir(str))
# ['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__',
# '__getattribute__', '__getitem__', '__getnewargs__', '__getstate__', '__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', 'removeprefix', 'removesuffix', 'replace', 'rfind', 'rindex',
# 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']4、获取字符串的帮助信息
用help()函数获取str的帮助信息
Help on class str in module builtins: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.| | Call keyword.iskeyword(s) to test whether string s is a reserved identifier,| such as "def" or "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.| | removeprefix(self, prefix, /)| Return a str with the given prefix string removed if present.| | If the string starts with the prefix string, return string[len(prefix):].| Otherwise, return a copy of the original string.| | removesuffix(self, suffix, /)| Return a str with the given suffix string removed if present.| | If the string ends with the suffix string and that suffix is not empty,| return string[:-len(suffix)]. Otherwise, return a copy of the original| string.| | 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 substrings in the string, using sep as the separator string.| | sep| The separator used to split the string.| | When set to None (the default value), will split on any whitespace| character (including \n \r \t \f and spaces) and will discard| empty strings from the result.| maxsplit| Maximum number of splits.| -1 (the default value) means no limit.| | Splitting starts at the end of the string and works 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 substrings in the string, using sep as the separator string.| | sep| The separator used to split the string.| | When set to None (the default value), will split on any whitespace| character (including \n \r \t \f and spaces) and will discard| empty strings from the result.| maxsplit| Maximum number of splits.| -1 (the default value) means no limit.| | Splitting starts at the front of the string and works to the end.| | Note, str.split() is mainly useful for data that has been intentionally| delimited. With natural text that includes punctuation, consider using| the regular expression module.| | 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 removed.| | 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(...)| 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.5、字符串的用法
5-1、capitalize()方法
# capitalize()方法：将字符串的第一个字符转换为大写，其余字符转换为小写，且不影响原始字符串
s = "hello, my Pyton World!"
s_capitalized = s.capitalize()
print(s_capitalized) # 输出: Hello, my pyton world!
print(s) # 输出: hello, my Pyton World!5-2、casefold()方法
# casefold()方法：将字符串中的所有字符转换为小写，并进行额外的折叠映射，以考虑不同语言环境的“大小写不敏感”比较，这与lower()方法有些相似，
# 但casefold()提供了更彻底的折叠，使得字符串在比较时更加“平等”
# 该方法不影响原始字符串
s = "Hello, my Python World!"
s_casefolded = s.casefold()
print(s_casefolded) # 输出：hello, my python world!
print(s) # 输出: Hello, my Python World!5-3、center()方法
# 1、方法：str.center
# 2、语法：str.center(width[, fillchar])
# 3、参数：
# 3-1、width(必需)：整数，表示新字符串的总宽度
# 3-2、fillchar(可选)：单个字符，用于填充新字符串的空白部分，默认为空格
# 4、功能：将字符串居中，并在其两侧填充指定的字符(默认为空格)
# 5、返回值：一个新的字符串
# 6、说明：
# 6-1、如果原始字符串的长度大于或等于width，则center()方法会返回原始字符串的副本
# 6-2、此方法不影响原始字符串
# 7、示例：
# 原始字符串
s = "myelsa"
# 使用center方法，总宽度为10，默认填充字符为空格
s_centered = s.center(10)
print(s_centered) # 输出:' myelsa '
# 使用center方法，总宽度为10，指定填充字符为'*'
s_centered_with_star = s.center(10, '*')
print(s_centered_with_star) # 输出: '**myelsa**'
# 注意原始字符串s并没有改变
print(s) # 输出: 'myelsa'5-4、count()方法
# 1、方法：str.count
# 2、语法：str.count(sub[, start[, end]])
# 3、参数：
# 3-1、sub：要搜索的子字符串
# 3-2、start(可选)：开始搜索的索引位置；默认为0，即字符串的开始
# 3-3、end(可选)：结束搜索的索引位置(不包括该位置)；默认为字符串的末尾
# 4、功能：用于计算子字符串在字符串中出现的次数
# 5、返回值：一个非负整数
# 6、说明：
# 6-1、如果子字符串在字符串中不存在，则返回0
# 6-2、当使用start和end参数时，count()方法只会计算在指定范围内子字符串出现的次数(遵守左闭右开原则)
# 7、示例：
# 原始字符串
s = "hello world, hello everyone"
# 计算子字符串 "hello" 出现的次数
count_hello = s.count("hello")
# 输出结果
print(count_hello) # 输出: 2
# 计算子字符串 "world" 出现的次数
count_world = s.count("world")
# 输出结果
print(count_world) # 输出: 1
# 计算子字符串 "python" 出现的次数(不存在)
count_python = s.count("python")
# 输出结果
print(count_python) # 输出: 0
# 使用start和end参数
count_hello_start_end = s.count("hello", 7, 20) # 只搜索索引7到20之间的部分(不包括20)
# 输出结果
print(count_hello_start_end) # 输出: 1，因为第二个 "hello" 在这个范围内5-5、encode()方法
# 1、方法：str.encode
# 2、语法：str.encode(encoding='utf-8', errors='strict')
# 3、参数：
# 3-1、encoding：指定字符编码的名称，默认为'utf-8'；Python支持多种字符编码，但最常用的是'utf-8'，它能够表示任何Unicode字符
# 3-2、errors：指定如何处理编码错误。默认是'strict'，表示如果无法编码某个字符，则抛出UnicodeEncodeError；
# 其他可能的值包括'ignore'(忽略无法编码的字符)、'replace'(用问号?替换无法编码的字符)和'xmlcharrefreplace'(使用XML字符引用替换无法编码的字符)
# 4、功能：用于将字符串转换为字节串(bytes)
# 5、返回值：一个字节串(bytes)
# 6、说明：
# 7、示例：
# 原始字符串
s = "Hello, World!"
# 编码为UTF-8字节串
b_utf8 = s.encode('utf-8')
# 打印字节串
print(b_utf8) # 输出: b'Hello, World!'
# 尝试使用不支持的编码
try:b_latin1 = s.encode('latin1') # 如果字符串中只包含Latin-1字符，这将成功print(b_latin1) # 输出：b'Hello, World!'
except UnicodeEncodeError as e:print(f"编码错误: {e}")
# 使用'replace'处理编码错误
s_with_non_ascii = "Hello, 世界!"
b_with_replacement = s_with_non_ascii.encode('ascii', 'replace')
# 打印带有替换字符的字节串
print(b_with_replacement) # 输出: b'Hello, ??!'5-6、endswith()方法
# 1、方法：str.endswith
# 2、语法：str.endswith(suffix[, start[, end]])
# 3、参数：
# 3-1、suffix(必须)：表示要检查的后缀
# 3-2、start(可选)：指定开始检查的起始位置(索引)；默认为0，即字符串的开始
# 3-3、end(可选)：指定结束检查的结束位置(索引)；默认为字符串的长度，即字符串的末尾
# 4、功能：用于检查字符串是否以指定的后缀结束
# 5、返回值：一个布尔值
# 6、说明：如果字符串以指定的后缀结束，则返回 True，否则返回 False
# 7、示例：
# 原始字符串
s = "Hello, World!"
# 检查字符串是否以"World!"结尾
is_endswith_world = s.endswith("World!")
print(is_endswith_world) # 输出: True
# 检查字符串是否以"Hello"结尾(不是)
is_endswith_hello = s.endswith("Hello")
print(is_endswith_hello) # 输出: False
# 检查字符串从索引5开始到结束是否以"World!"结尾(是)
is_endswith_world_from_index5 = s.endswith("World!", 7) # 注意：索引7是"W"的位置，但不影响结果
print(is_endswith_world_from_index5) # 输出: True
# 检查字符串从索引0开始到索引10是否以"ello"结尾(不是)
is_endswith_ello = s.endswith("ello", 0, 11) # 注意：索引11超出了字符串长度，但不影响检查到索引10的部分
print(is_endswith_ello) # 输出: False5-7、expandtabs()方法
# 1、方法：str.expandtabs
# 2、语法：str.expandtabs([tabsize=8])
# 3、参数：
# 3-1、tabsize(可选)：表示一个制表符应该由多少个空格代替；默认值是8，这通常是大多数系统中制表符的标准宽度
# 4、功能：用于将字符串中的制表符(\t)替换为一定数量的空格，从而扩展它们以匹配指定的制表符宽度
# 5、返回值：返回一个新的字符串
# 6、说明：expandtabs()方法返回一个新的字符串，而原始字符串保持不变
# 7、示例：
# 使用默认的制表符宽度(8个空格)
s = "Hello\tWorld"
expanded_s = s.expandtabs()
print(expanded_s) # 输出: Hello World
# 使用自定义的制表符宽度(4个空格)
s = "Hello\tWorld"
expanded_s = s.expandtabs(tabsize=11)
print(expanded_s) # 输出: Hello World
# 字符串中有多个制表符
s = "Hello\t\tWorld"
expanded_s = s.expandtabs()
print(expanded_s) # 输出: Hello World5-8、find()方法
# 1、方法：str.find
# 2、语法：str.find(sub[, start[, end]])
# 3、参数：
# 3-1、sub(必需)：表示要查找的子字符串
# 3-2、start(可选)：表示开始查找的位置索引；默认值为0，表示从字符串的开始位置查找
# 3-3、end(可选)：表示结束查找的位置索引；默认值为字符串的长度，表示查找到字符串的末尾
# 4、功能：用于查找子字符串在主字符串中首次出现的位置索引
# 5、返回值：返回子字符串在主字符串中首次出现的位置索引
# 6、说明：
# 6-1、当指定了起始索引时，find()方法将从该索引开始查找
# 6-2、如果未找到子字符串，或者起始索引大于结束索引，则find()方法返回-1
# 7、示例：
# 查找子字符串首次出现的位置
s = "Hello, World!"
index = s.find("World")
print(index) # 输出: 7
# 查找子字符串首次出现的位置(指定起始索引)
index = s.find("World", 6) # 从索引6开始查找
print(index) # 输出: 7
# 查找不存在的子字符串
index = s.find("Python")
print(index) # 输出: -1
# 查找子字符串在指定范围内的位置
index = s.find("o", 1, 5) # 从索引1开始到索引5结束(不包括索引5)查找'o'
print(index) # 输出: 4
# 如果起始索引大于结束索引，find()会返回 -1
index = s.find("o", 10, 5)
print(index) # 输出: -15-9、format()方法
# 在Python中，字符串的format()方法提供了一种灵活的方式来格式化字符串
# format()方法可以与字符串字面量中的大括号`{}`占位符一起使用，或者与`str.format()`方法一起使用来插入和格式化变量值
# 1、基本用法
# 使用`{}`占位符，并在调用`format()`方法时提供参数：
name = "Myelsa"
age = 18
formatted_string = "My name is {} and I am {} years old.".format(name, age)
print(formatted_string) # 输出: My name is Myelsa and I am 18 years old.
# 2、命名参数
# 在`{}`中使用变量名来引用参数：
name = "Bruce"
formatted_string = "Hello, {name}!".format(name=name)
print(formatted_string) # 输出: Hello, Bruce!
# 3、位置参数
# 使用位置参数，与占位符的顺序对应：
name = "Jimmy"
age = 15
formatted_string = "Name: {}, Age: {}".format(name, age)
print(formatted_string) # 输出: Name: Jimmy, Age: 15
# 4、格式化数字
# 使用冒号`:`后的格式说明符来格式化数字：
pi = 3.141592653589793
formatted_string = "Pi is approximately {:.4f}".format(pi)
print(formatted_string) # 输出: Pi is approximately 3.1416
# 5、格式说明符
# 5-1、`{}`:占位符
# 5-2、`:`:开始格式说明符
# 5-3、`.`(可选):用于指定小数点后的精度
# 5-4、`<`, `>`, `^`(可选)：用于指定对齐方式(左对齐、右对齐、居中对齐)
# 5-5、`+`(可选):用于在数字前显示正负号
# 5-6、`-`(可选):用于左对齐(默认是右对齐)
# 5-7、空格(可选):在正数前加一个空格
# 5-8、`#`(可选)：用于二进制、八进制、十六进制表示，以及浮点数的小数点和指数
# 5-9、`0`(可选)：用于指定填充的字符(如果指定了宽度)
# 5-10、数字(可选)：指定最小宽度
# 5-11类型(可选)：如`f`(浮点数)、`s`(字符串)、`d`(整数)等# 6、嵌套和复杂用法
# `format()`方法还支持更复杂的嵌套和格式化，例如访问列表、字典或对象的属性：
person = {"name": "Jimmy", "age": 15, "city": "Foshan"}
formatted_string = "My name is {name}, I am {age} years old, and I live in {city}.".format(**person)
print(formatted_string) # 输出: My name is Jimmy, I am 15 years old, and I live in Foshan.
# 7、访问列表中的元素
items = ["apple", "banana", "cherry"]
formatted_string = "I have {} items: {}".format(len(items), ", ".join(items))
print(formatted_string) # 输出: I have 3 items: apple, banana, cherry# 8、f-string(Python 3.6+)
# 从Python 3.6开始，可以使用f-string(格式化字符串字面量)作为另一种更简洁、易读的字符串格式化方法：
name = "Myelsa"
age = 18
formatted_string = f"My name is {name} and I am {age} years old."
print(formatted_string) # 输出: My name is Myelsa and I am 18 years old.
# f-string允许在字符串中直接嵌入表达式，并在运行时求值，这使得字符串格式化更加简洁和直观5-10、format_map()方法
# 1、方法：str.format_map
# 2、语法：str.format_map(mapping)
# 3、参数：
# 3-1、mapping(必需)：表示映射类型，如字典等
# 4、功能：接受一个映射类型作为参数，并使用映射类型中的键值对来替换字符串中的格式化字段
# 5、返回值：一个新的字符串
# 6、说明：注意，format_map()方法只能处理字典或其他映射类型中的键值对，与 str.format()方法相比，它提供了一种更简洁、更直观的方式来使用字典进行字符串格式化
# 7、示例：
# 定义一个包含要格式化的数据的字典
data = {'name': 'Myelsa','age': 18,'city': 'Guangzhou'
}
# 定义一个带有格式化字段的字符串模板
template = 'My name is {name}, I am {age} years old, and I live in {city}.'
# 使用format_map()方法来格式化字符串
formatted_string = template.format_map(data)
# 输出格式化后的字符串
print(formatted_string) # 输出：My name is Myelsa, I am 18 years old, and I live in Guangzhou.5-11、index()方法
# 1、方法：str.index
# 2、语法：str.index(sub[, start[, end]])
# 3、参数：
# 3-1、sub(必需)：表示要查找的子字符串
# 3-2、start(可选)：表示开始查找的位置索引；默认值为0，表示从字符串的开始位置查找
# 3-3、end(可选)：表示结束查找的位置索引；默认值为字符串的长度，表示查找到字符串的末尾
# 4、功能：用于查找子字符串在主字符串中首次出现的位置索引
# 5、返回值：一个正整数
# 6、说明：
# 6-1、如果start参数大于end参数，或者sub参数在主字符串中不存在，index()方法会抛出一个ValueError异常；因此，在使用index()方法时，最好使用try-except块来捕获并处理可能的异常
# 6-2、与find()方法不同，index()方法在找不到子字符串时会抛出ValueError异常，而find()方法会返回-1
# 7、示例：
s = "Hello, World!"
# 查找子字符串首次出现的位置
index = s.index("World")
print(index) # 输出: 7
# 查找子字符串首次出现的位置(指定起始索引)
index = s.index("World", 8) # 注意：这里会抛出ValueError，因为从索引8开始找不到"world"
# print(index) # 这行代码会抛出 ValueError: substring not found
# 查找不存在的子字符串
try:index = s.index("Python")print(index)
except ValueError:print("Substring not found") # 输出: Substring not found
# 查找子字符串在指定范围内的位置
index = s.index("o", 1, 5) # 从索引1开始到索引5结束(不包括索引5)查找'o'
print(index) # 输出: 45-12、isalnum()方法
# 1、方法：str.isalnum
# 2、语法：str.isalnum()
# 3、参数：无
# 4、功能：用于检查字符串中的所有字符是否都是字母(alphabetic)或数字(numeric)，并且字符串至少包含一个字符
# 5、返回值：一个布尔值
# 6、说明：
# 6-1、如果字符串中所有字符都是字母或数字，则返回True，否则返回False
# 6-2、isalnum()方法只会检查字符串中的字符是否是字母或数字，而不会考虑字符的大小写(即大写字母和小写字母都被视为字母)
# 6-3、该方法也不会考虑字符串中的空白字符(如空格、制表符、换行符等)，因此即使字符串中包含一个空格，isalnum()也会返回False
# 6-4、如果参数为空，isalnum()会返回False
# 7、示例：
s1 = "Hello 123"
print(s1.isalnum()) # 输出: False，因为包含非字母非数字的字符(空格)
s2 = "Hello 123"
print(s2.replace(" ", "").isalnum()) # 输出: True，移除空格后，所有字符都是字母或数字
s3 = "12345"
print(s3.isalnum()) # 输出: True，所有字符都是数字
s4 = "abcdef"
print(s4.isalnum()) # 输出: True，所有字符都是字母
s5 = "Hello World"
print(s5.isalnum()) # 输出: False，包含空格
s6 = "Hello123!"
print(s6.isalnum()) # 输出: False，包含非字母非数字的字符(感叹号)
s7 = ""
print(s7.isalnum()) # 输出: False，空字符串5-13、isalpha()方法
# 1、方法：str.isalpha
# 2、语法：str.isalpha()
# 3、参数：无
# 4、功能：用于检查字符串中的所有字符是否都是字母，并且至少包含一个字符
# 5、返回值：一个布尔值
# 6、说明：
# 6-1、如果字符串中所有字符都是字母，则返回True，否则返回False
# 6-2、isalpha()方法只考虑字母字符，包括大写和小写字母，它不会考虑数字、空白字符(如空格、制表符、换行符等)或其他特殊字符
# 6-3、如果参数为空，isalpha()会返回False
# 7、示例：
s1 = "Hello"
print(s1.isalpha()) # 输出: True，因为所有字符都是字母
s2 = "Hello123"
print(s2.isalpha()) # 输出: False，因为包含数字
s3 = "Hello World"
print(s3.isalpha()) # 输出: False，因为包含空格
s4 = "Hello!"
print(s4.isalpha()) # 输出: False，因为包含非字母字符(感叹号)
s5 = ""
print(s5.isalpha()) # 输出: False，空字符串
s6 = "12345"
print(s6.isalpha()) # 输出: False，所有字符都是数字
s7 = "Helloもじ"
print(s7.isalpha()) # 输出: True 因为所有字符都是字母，即使字母是用日文表示5-14、isascii()方法
# 1、方法：str.isdecimal
# 2、语法：str.isdecimal()
# 3、参数：无
# 4、功能：用于检查字符串中的所有字符是否都是十进制数字，且至少有一个这样的字符
# 5、返回值：一个布尔值
# 6、说明：
# 6-1、如果字符串中的所有字符都是十进制数字则返回True，否则返回False
# 6-2、isdecimal()方法只检查字符串中的字符是否属于Unicode十进制数字类别，它不会识别像罗马数字、中文数字或其他非标准的数字表示形式
# 6-3、如果你需要更广泛的数字检测(包括小数点、负号等)，你可能需要使用正则表达式或其他字符串处理方法
# 7、示例：
s1 = "12345"
print(s1.isdecimal()) # 输出: True，因为所有字符都是十进制数字
s2 = "12345a"
print(s2.isdecimal()) # 输出: False，因为包含非数字字符
s3 = "123.45"
print(s3.isdecimal()) # 输出: False，因为包含小数点
s4 = ""
print(s4.isdecimal()) # 输出: False，空字符串不包含任何十进制数字字符
s5 = "⅛" #（这里使用的是分数形式的数字）
print(s5.isdecimal()) # 输出: False，因为包含非十进制数字字符5-15、isdigit()方法
# 1、方法：str.isdigit
# 2、语法：str.isdigit()
# 3、参数：无
# 4、功能：用于检查字符串中的所有字符是否都是数字字符，且至少有一个这样的字符
# 5、返回值：一个布尔值
# 6、说明：
# 6-1、如果字符串中的所有字符都是数字字符则返回 True，否则返回 False
# 6-2、isdigit() 方法只检查字符串中的字符是否属于标准的数字字符(即0-9)，它不会识别像罗马数字、中文数字或其他非标准的数字表示形式
# 6-3、如果你需要更广泛的数字检测(包括小数点、负号等)，你可能需要使用正则表达式或其他字符串处理方法
# 7、示例：
s1 = "12345"
print(s1.isdigit()) # 输出: True，因为所有字符都是数字字符
s2 = "12345a"
print(s2.isdigit()) # 输出: False，因为包含非数字字符
s3 = "123.45"
print(s3.isdigit()) # 输出: False，因为包含小数点
s4 = ""
print(s4.isdigit()) # 输出: False，空字符串不包含任何数字字符
s5 = "⅛" #（这里使用的是分数形式的数字）
print(s5.isdigit()) # 输出: False，因为包含非数字字符
