python入门到放弃(四)-基本数据类型之str字符串
1.概念
python中用',",''',"""引起来的内容称为字符串，可以保存少量数据并进行相应的操作
#先来看看str的源码写了什么，方法:按ctrl+鼠标左键点str
class int(object): """ int(x=0) -> int or long int(x, base=10) -> int or long Convert a number or string to an integer, or return 0 if no arguments are given. If x is floating point, the conversion truncates towards zero. If x is outside the integer range, the function returns a long instead. If x is not a number or if base is given, then x must be a string or Unicode object representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal. >>> int('0b100', base=0) """ def bit_length(self): """ 返回表示该数字的时占用的最少位数 """ """ int.bit_length() -> int Number of bits necessary to represent self in binary. >>> bin(37) '0b100101' >>> (37).bit_length() """ return 0 def conjugate(self, *args, **kwargs): # real signature unknown """ 返回该复数的共轭复数 """ """ Returns self, the complex conjugate of any int. """ pass def __abs__(self): """ 返回绝对值 """ """ x.__abs__() <==> abs(x) """ pass def __add__(self, y): """ x.__add__(y) <==> x+y """ pass def __and__(self, y): """ x.__and__(y) <==> x&y """ pass def __cmp__(self, y): """ 比较两个数大小 """ """ x.__cmp__(y) <==> cmp(x,y) """ pass def __coerce__(self, y): """ 强制生成一个元组 """ """ x.__coerce__(y) <==> coerce(x, y) """ pass def __divmod__(self, y): """ 相除，得到商和余数组成的元组 """ """ x.__divmod__(y) <==> divmod(x, y) """ pass def __div__(self, y): """ x.__div__(y) <==> x/y """ pass def __float__(self): """ 转换为浮点类型 """ """ x.__float__() <==> float(x) """ pass def __floordiv__(self, y): """ x.__floordiv__(y) <==> x//y """ pass def __format__(self, *args, **kwargs): # real signature unknown pass def __getattribute__(self, name): """ x.__getattribute__('name') <==> x.name """ pass def __getnewargs__(self, *args, **kwargs): # real signature unknown """ 内部调用 __new__方法或创建对象时传入参数使用 """ pass def __hash__(self): """如果对象object为哈希表类型，返回对象object的哈希值。哈希值为整数。在字典查找中，哈希值用于快速比较字典的键。两个数值如果相等，则哈希值也相等。""" """ x.__hash__() <==> hash(x) """ pass def __hex__(self): """ 返回当前数的 十六进制 表示 """ """ x.__hex__() <==> hex(x) """ pass def __index__(self): """ 用于切片，数字无意义 """ """ x[y:z] <==> x[y.__index__():z.__index__()] """ pass def __init__(self, x, base=10): # known special case of int.__init__ """ 构造方法，执行 x = 123 或 x = int(10) 时，自动调用，暂时忽略 """ """ int(x=0) -> int or long int(x, base=10) -> int or long Convert a number or string to an integer, or return 0 if no arguments are given. If x is floating point, the conversion truncates towards zero. If x is outside the integer range, the function returns a long instead. If x is not a number or if base is given, then x must be a string or Unicode object representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal. >>> int('0b100', base=0) # (copied from class doc) """ pass def __int__(self): """ 转换为整数 """ """ x.__int__() <==> int(x) """ pass def __invert__(self): """ x.__invert__() <==> ~x """ pass def __long__(self): """ 转换为长整数 """ """ x.__long__() <==> long(x) """ pass def __lshift__(self, y): """ x.__lshift__(y) <==> x<<y """ pass def __mod__(self, y): """ x.__mod__(y) <==> x%y """ pass def __mul__(self, y): """ x.__mul__(y) <==> x*y """ pass def __neg__(self): """ x.__neg__() <==> -x """ pass @staticmethod # known case of __new__ def __new__(S, *more): """ T.__new__(S, ...) -> a new object with type S, a subtype of T """ pass def __nonzero__(self): """ x.__nonzero__() <==> x != 0 """ pass def __oct__(self): """ 返回改值的 八进制 表示 """ """ x.__oct__() <==> oct(x) """ pass def __or__(self, y): """ x.__or__(y) <==> x|y """ pass def __pos__(self): """ x.__pos__() <==> +x """ pass def __pow__(self, y, z=None): """ 幂，次方 """ """ x.__pow__(y[, z]) <==> pow(x, y[, z]) """ pass def __radd__(self, y): """ x.__radd__(y) <==> y+x """ pass def __rand__(self, y): """ x.__rand__(y) <==> y&x """ pass def __rdivmod__(self, y): """ x.__rdivmod__(y) <==> divmod(y, x) """ pass def __rdiv__(self, y): """ x.__rdiv__(y) <==> y/x """ pass def __repr__(self): """转化为解释器可读取的形式 """ """ x.__repr__() <==> repr(x) """ pass def __str__(self): """转换为人阅读的形式，如果没有适于人阅读的解释形式的话，则返回解释器课阅读的形式""" """ x.__str__() <==> str(x) """ pass def __rfloordiv__(self, y): """ x.__rfloordiv__(y) <==> y//x """ pass def __rlshift__(self, y): """ x.__rlshift__(y) <==> y<<x """ pass def __rmod__(self, y): """ x.__rmod__(y) <==> y%x """ pass def __rmul__(self, y): """ x.__rmul__(y) <==> y*x """ pass def __ror__(self, y): """ x.__ror__(y) <==> y|x """ pass def __rpow__(self, x, z=None): """ y.__rpow__(x[, z]) <==> pow(x, y[, z]) """ pass def __rrshift__(self, y): """ x.__rrshift__(y) <==> y>>x """ pass def __rshift__(self, y): """ x.__rshift__(y) <==> x>>y """ pass def __rsub__(self, y): """ x.__rsub__(y) <==> y-x """ pass def __rtruediv__(self, y): """ x.__rtruediv__(y) <==> y/x """ pass def __rxor__(self, y): """ x.__rxor__(y) <==> y^x """ pass def __sub__(self, y): """ x.__sub__(y) <==> x-y """ pass def __truediv__(self, y): """ x.__truediv__(y) <==> x/y """ pass def __trunc__(self, *args, **kwargs): """ 返回数值被截取为整形的值，在整形中无意义 """ pass def __xor__(self, y): """ x.__xor__(y) <==> x^y """ pass denominator = property(lambda self: object(), lambda self, v: None, lambda self: None) # default """ 分母 = 1 """ """the denominator of a rational number in lowest terms""" imag = property(lambda self: object(), lambda self, v: None, lambda self: None) # default """ 虚数，无意义 """ """the imaginary part of a complex number""" numerator = property(lambda self: object(), lambda self, v: None, lambda self: None) # default """ 分子 = 数字大小 """ """the numerator of a rational number in lowest terms""" real = property(lambda self: object(), lambda self, v: None, lambda self: None) # default """ 实属，无意义 """ """the real part of a complex number""" int
2.字符串的索引和切片
#索引
#索引就是下标，切记，下标从0开始 s = "大河向东流去" print(s[0]) #大 #从0开始取 print(s[1]) #河 print(s[2]) #向 print(s[3]) #东 print(s[4]) #流 print(s[5]) #去 print(s[6]) #索引不能超过边界，要不然会报错 print(s[-1]) #-1就是倒着从后面取 print(s[-2]) print(s[-3]) print(s[-4]) print(s[-5]) print(s[-6])
#切片
#切片[起始位置：结束位置] #特点：1、顾头不顾尾 2、只能从左往右切 #例子： s = "改革春风吹满面"
print(s[1:3]) #从1切到3，但是取不到3
#革春 #因为是下标从0开始，所以1就是革
print(s[1:]) #从1开始切，切到结尾 #革春风吹满面
print(s[:2]) #从头开始切到2
#改革
print(s[:]) #从头到尾
#改革春风吹满面
print(s[-1:-3]) #这样从右往左切会是空值 print(s[-3:-1]) #只能从左往右切
#吹满
#跳着取值，步长
#步长：如果是整数，就从左往右取，如果是负数就从右往左取 print(s[-1:-3:-1]) # - 表示反方向，从右往左 print(s[3:9:2]) #表示3到9中间每隔2位取一个 print(s[4:10:3]) #表示4到10中间每隔3取一位 print(s[-3:-9:-2]) #从右往左每个2位取一个
3.字符串相关操作
#注意点：
#注意：字符串是不可变的对象，所有任何操作对源字符串是不会有任何影响的 #例如 s = "I am a teacher" s.capitalize() print(s) #I am a teacher
#1.大小写的相互转换
#关键字 # capitalize():将首字母变成大写 # lower():全部替换成小写 # upper():全部替换成大写 # swapcase():大小写互换 # casefold():转换成小写 # titile():每个被特殊字符隔开的首字母大写
#例子：
s = "This is teacher and Student" s1 = s.capitalize() #将首字母变成大写 print(s1) #This is teacher and student s2 = s.lower() #全部转换成小写 print(s2) #this is teacher and student s3 = s.upper() #全部转换成大写 print(s3) #THIS IS TEACHER AND STUDENT s4 = s.swapcase() #大小写互相转换 print(s4) #tHIS IS TEACHER AND sTUDENT s5 = s.casefold() #转换成小写，这个能识别出所有字母，但lower有些不支持 print(s5) #this is teacher and student
#2.切来切去
#关键字 # center():内容居中 # strip():去掉左右两端的空格 # lstrip():去掉左边的空格 # rstrip():去掉右边的空格 # replace（old,new）：字符替换 # split（）：切割
#例子：
#1.拉长的长度:center() s = "nb" s1 = s.center(10,"#") #强行使用#号在原字符串左右两端进行拼接，拼接成10个单位 print(s1) # 更改tab的长度 s6 = "alex wusir\teggon" print(s6) print(s6.expandtabs()) # 可以改变\t的⻓长度, 默认⻓长度更更改为8 #2.去空格 s = " guoke boy is " s1 = s.strip() #默认去掉两边的空格 print(s1) #打印出来的时候就会发现两边没有空格 s2 = s.lstrip() #去掉左边的空格 print(s2) s3 = s.rstrip() #去掉右边的空格 print(s3) #strip()应用 # 设置用户交互式登陆的时候，如果不加strip()，当用户如输入用户名后面加了空格，那么就会报错 # 如果加了strip(),就可以去掉两边的空格 username = input("请输入用户名:").strip() password = input("请输入密码:").strip() if username == 'cw' and password == '123': print("登陆成功") else: print("登陆失败") #指定去掉的元素 s = "nb boy guoke nb nb tiantian sb" print(s.strip("nb")) #3.字符串替换:replace() s = "student，战狼，teacher,小猪佩奇_eat，少年的你" s1 = s.replace("少年的你","中国机长") #将少年的你替换成中国机长 s2 = s.replace("小猪","猫猫") #将小猪替换成猫猫 print(s1,s2) s3 = s.replace('e','nb',2) #将e替换成nb，替换前两个 print(s3) #4.字符串切割：split() s4 = "fd,fwe,tet,rer,aggo" lst = s4.split(",") #字符串切割，根据,进行切割 print(lst) s5 = s4.split("e") #使用什么进行切割就会损失掉什么 print(s5) #坑点 # s7 = "湖边哈哈美丽美丽湖人湖边" # lst = s7.split("湖边") #如果切割符在左右两端，那么一定会出现空字符串 # print(lst) # print(bool(lst)) #可以看到返回是True,因为是空字符串
#3.查找相关
#关键字: # startswith():判断是否以xxx开头 # endswith():判断是否以xxx结尾 # count():查看那个字符出现的次数 # find():查看关键字在什么位置，没有找到的话就返回-1 # index():求索引的位置：如果没找到字符串就会报错
#例子：
s = "我是一个boy，我喜欢python，java等编程语言" s1 = s.startswith("我是一个") #判断是否以我开头，如果是就会返回True，否则返回False print(s1) #True s2 = s.startswith("boy") #可以看出返回的结果是False print(s2) #False s3 = s.endswith("语言") #判断是否以"语言"位结尾，是就会返回True，否则返回False print(s3) #True s4 = s.endswith("我们") #可以看出不是以我们结尾就返回False print(s4) #False s5 = s.count("a") #统计"a"出现的次数 print(s5) #2 s6 = s.find("java") #查看Java出现的位置,只找第一次出现的位置，没有就返回-1 print(s6) #18 s7 = s.find("a",20,29) #切片找，指定位置找a，从20-29中间找有没有a print(s7) #21 s8 = s.index("java") #查找java的位置 print(s8) #18 # s9 = s.index("z") #index如果没有查找到的话就会报错，写程序的就不用使用index，否则整个程序都会崩掉了，使用find # print(s9)
#4.条件判断相关
#关键字 # isalnum():判断是否由字母和数字组成 # isalpha():判断是否由字母组成 # isdigit():判断是否由数字组成 # isdecimal():判断是否由数字组成 # isnumeric():判断是否由数字组成 #中文也识别
#例子：
s1 = "12345" s2 = "123abc" s3 = "abcde" s4 = "_abdf@" s5 = "壹仟叁佰肆拾" print(s1.isdigit()) #判断是否由数字组成，如果是就返回True，否则Fase #True print(s2.isalnum()) #判断是否由数字和字母组成 #True print(s3.isalpha()) #判断是否由字母组成 #True print(s5.isnumeric()) #判断是否由数字组成，可以是大写的，如果是字符串就报错 #True print(s1.isdecimal()) #判断是否由数字组成 #True #练习，用算法判断某一个字符串是否是小数 s17 = "-123.12" s17 = s17.replace("-", "") # 替换掉负号 if s17.isdigit(): print("是整数") else: if s17.count(".") == 1 and not s17.startswith(".") and not s17.endswith("."): print("是⼩小数") else: print("不不是⼩小数") #过程理解：首先将符号替换成空字符串，然后进入判断变量是否是数字组成 #很显然是没有由数字组成，所有就走else,又进入如果判断，如果统计点符号等于1 #和不是以点开头和不是以点结尾，满足条件，所以打印是小小数
#5.计算字符串的长度
#关键字 #len():计算机字符串的长度
#例子：
s1 = "我是你的小呀小苹果" ret = len(s1) print(ret) #9 #注意：len()是python的内置函数，所以访问方式也不一样，记住len()和print()方式一样
#6.join
#join:将列表转换成字符串 #注意:join(里面放的是可迭代对象)
#例子
lst = ["蒋小雨","张冲","鲁炎"] s = "_".join(lst) print(s) #蒋小雨_张冲_鲁炎 s = "_".join("武黑脸") print(s) #武_黑_脸 #将字符串转换成列表：split() s = "马云,移动,雷子" lst = s.split(",") print(lst) #['马云', '移动', '雷子']
