Python之一些容易被忽略的小细节（一） - 好文

        字符串操作

      一、大小写转换

      1. capitalize()：第一个字母大写。
s = 'aBcDeFg' s1 = s.capitalize() print(s1)
      运行结果：

Abcdefg

Process finished with exit code 0

      2. lower()：全部换为小写。
s = 'aBcDeFg' s1 = s.lower() print(s1)
      运行结果：

abcdefg

Process finished with exit code 0

        3. upper()：全部转化为大写。
s = 'aBcDeFg' s1 = s.upper() print(s1)        运行结果：
ABCDEFG

Process finished with exit code 0

      4. swapcase()：大小写相互转化。
s = 'aBcDeFg' # 第一次转 s1 = s.swapcase() print(s1) # 第二次转 s2 = s1.swapcase()
print(s2)
        运行结果：

AbCdEfG
aBcDeFg

Process finished with exit code 0

      5. casefold()：除了英文外，将其他字符小写，效率略低，建议少用。
s2 = "БBß" # 俄美德 print(s2) print(s2.lower()) print(s2.casefold())      运行结果：

БBß
бbß
бbss

Process finished with exit code 0

      6. title()：每个单词首字母大写，被特殊字符隔开也算。
s3 = "hello eggon,java*nodejs_麻花藤dashabi" ret = s3.title() print(ret)
        运行结果：

Hello Eggon,Java*Nodejs_麻花藤Dashabi

Process finished with exit code 0

      二、字符串切割

      1. center(居中长度,“空白覆盖”)：居中。
s5 = "周杰伦" ret = s5.center(10, "*") # 拉长成10, 把原字符串放中间.其余位置补* print(ret)
      运行结果：

***周杰伦****

Process finished with exit code 0

      说明：若是居中长度小于字符串长度，原样打印字符串。若是刚好不是正中间，优先往左靠一个字符（尽量居中）。

      2. 去空格strip(),lstrip(),rstrip()：去左右两边空白，去左空白，去右空白。
s7 = " python nodejs java " ret = s7.strip() # 去掉左右两端的空格 print(ret) ret = s7
.lstrip()# 去掉左边空格 print(ret) ret = s7.rstrip() # 去掉右边空格 print(ret)
        运行结果：

python nodejs java
python nodejs java
python nodejs java

Process finished with exit code 0

      strip()也可以去掉指定的元素。
s7 = "abcdefgabc" print(s7.strip("abc")) print(s7.strip("ef")) # 无法去除中间元素
      运行结果：

defg
abcdefgabc

Process finished with exit code 0

      3. replace()：字符串替换。
s8 = "Hello,Hold your dream" ret = s8.replace('your', 'our') print(ret)
      运行结果：

Hello,Hold our dream

Process finished with exit code 0

      4. split()：字符串切割。
s = "Hello,Hold your dream" ret = s.split("o") print(ret)
      运行结果：

['Hell', ',H', 'ld y', 'ur dream']

Process finished with exit code 0

      说明：切割之后返回列表。

      三、字符串查找

      1. startswith()，endswith()：判断是否以某字符（串）开头或者结尾，返回值为布尔类型。
s = "Hello,Hold your dream" print(s.startswith("H")) print(s.endswith("M"))
      运行结果：

True
False

Process finished with exit code 0

      2. count()：查找字符（串）出现的次数
s = "Hello,Hold your dream" re = s.count("o") print(re)
      运行结果：

3

Process finished with exit code 0

      3. find()：查找字符（串）的位置。
s = "Hello,Hold your dream" re = s.find("Ho") print(re)
      运行结果：

6

Process finished with exit code 0

      注意：返回的是字符串的第一个值的角标。

      4. index()：找到字符串索引位置。
s = "Hello,Hold your dream" re = s.index("Ho") # re1 = s.index("Hl") #
ValueError: substring not foundprint(re)
      运行结果：

6

Process finished with exit code 0

  和index()不同的是find()在找不到substring时不会抛出异常，而是会返回-1，因此不会影响程序的执行。
s = "Hello,Hold your dream" re = s.index("Ho") re1 = s.find("Hl") # 不会抛出错误，返回-1
print(re) print(re1)
      运行结果：
6
-1

Process finished with exit code 0

      三、列表操作

      1. 切片
lst = ["麻花藤", "王剑林", "马芸", "周鸿医", "向华强"] print(lst[0:3]) # ['麻花藤', '王剑林', '马芸']
print(lst[:3]) # ['麻花藤', '王剑林', '马芸'] print(lst[1::2]) # ['王剑林', '周鸿医'] 也有步长
print(lst[2::-1]) # ['马芸', '王剑林', '麻花藤'] 也可以倒着取 print(lst[-1:-3:-2]) # 倒着带步长
      运行结果：

['麻花藤', '王剑林', '马芸']
['麻花藤', '王剑林', '马芸']
['王剑林', '周鸿医']
['马芸', '王剑林', '麻花藤']
['向华强']

Process finished with exit code 0

      2. 删除pop()，remove()，clear()，del()的练习与区别。
lst = ["麻花藤", "王剑林", "李嘉诚", "王富贵"] print(lst) deleted = lst.pop() # 删除最后一个
print("被删除的", deleted) print(lst) el = lst.pop(2) # 删除2号元素 print(el) print(lst)
lst.remove("麻花藤") # 删除指定元素 print(lst) # lst.remove("哈哈") # 删除不存在的元素会报错 # #
print(lst)lst.clear() # 清空list print(lst) # 切⽚删除，删除角标为1和2的元素 del lst[1:3] print(
lst)
        运行结果：

['麻花藤', '王剑林', '李嘉诚']
李嘉诚
['麻花藤', '王剑林']
['王剑林']
[]
[]

Process finished with exit code 0

      3. 修改
lst = ["Python", "Java", "Golang", "Perl", "JavaScript", "Node.js", "C#", "D"]
#修改 lst[3] = "C++" print(lst) # 切片修改，步长为3,注意取值的个数 lst[1:4:3] = ["VB"] print(lst)
#切片修改，步长为默认值1 lst[1:4] = ["I like Python"] print(lst)
        运行结果：

['Python', 'Java', 'Golang', 'C++', 'JavaScript', 'Node.js', 'C#', 'D']
['Python', 'VB', 'Golang', 'C++', 'JavaScript', 'Node.js', 'C#', 'D']
['Python', 'I like Python', 'JavaScript', 'Node.js', 'C#', 'D']

Process finished with exit code 0

      4. 迭代查询
lst = ["Python", "Java", "Golang", "Perl", "JavaScript", "Node.js", "C#", "D"]
forel in lst: print(el)
        运行结果：

Python
Java
Golang
Perl
JavaScript
Node.js
C#
D

Process finished with exit code 0

      5. 其它操作

      reverse()：列表翻转
lst = ["Python", "Java", "Golang", "Perl", "JavaScript", "Node.js", "C#", "D"]
lst.reverse() print(lst)      运行结果：

['D', 'C#', 'Node.js', 'JavaScript', 'Perl', 'Golang', 'Java', 'Python']

Process finished with exit code 0

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