Python之一些容易被忽略的小细节（一）

- 日理万妓 2022-05-20 06:34 396阅读 0赞

字符串操作

一、大小写转换

1. capitalize()：第一个字母大写。

  1. s = 'aBcDeFg'
  2. s1 = s.capitalize()
  3. print(s1)

运行结果：

Abcdefg

Process finished with exit code 0

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

abcdefg

Process finished with exit code 0 

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

ABCDEFG

Process finished with exit code 0 

  1.     4. swapcase()：大小写相互转化。
  3. s = 'aBcDeFg'
  4. # 第一次转
  5. s1 = s.swapcase()
  6. print(s1)
  7. # 第二次转
  8. s2 = s1.swapcase()
  9. print(s2)
  11.     运行结果：

AbCdEfG
aBcDeFg

Process finished with exit code 0

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

БBß
бbß
бbss

Process finished with exit code 0

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

Hello Eggon,Java*Nodejs_麻花藤Dashabi

Process finished with exit code 0 

  1.     **二、字符串切割**  
  4.     1. center(居中长度,“空白覆盖”)：居中。
  6. s5 = "周杰伦"
  7. ret = s5.center(10, "*")  # 拉长成10, 把原字符串放中间.其余位置补*
  8. print(ret)
  10.     运行结果：

***周杰伦****

Process finished with exit code 0 

  1.     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）。  
  4.     2. 去空格strip(),lstrip(),rstrip()：去左右两边空白，去左空白，去右空白。
  6. s7 = " python nodejs java "
  7. ret = s7.strip()  # 去掉左右两端的空格
  8. print(ret)
  9. ret = s7.lstrip()  # 去掉左边空格
  10. print(ret)
  11. ret = s7.rstrip()  # 去掉右边空格
  12. print(ret)
  14.     运行结果：

python nodejs java
python nodejs java
python nodejs java

Process finished with exit code 0

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

defg
abcdefgabc

Process finished with exit code 0 

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

Hello,Hold our dream

Process finished with exit code 0

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

[‘Hell’, ‘,H’, ‘ld y’, ‘ur dream’]

Process finished with exit code 0

  1.     说明：切割之后返回列表。  
  4.     **三、字符串查找**  
  7.     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。
  9. s = "Hello,Hold your dream"
  10. print(s.startswith("H"))
  11. print(s.endswith("M"))
  13.     运行结果：

True
False

Process finished with exit code 0 

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

3

Process finished with exit code 0

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

6

Process finished with exit code 0

  1.     注意：返回的是字符串的第一个值的角标。  
  4.     4. index()：找到字符串索引位置。        
  6. s = "Hello,Hold your dream"
  7. re = s.index("Ho")
  8. # re1 = s.index("Hl") # ValueError: substring not found
  9. print(re)
  11.     运行结果：

6

Process finished with exit code 0

  1.     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。
  3. s = "Hello,Hold your dream"
  4. re = s.index("Ho")
  5. re1 = s.find("Hl")  # 不会抛出错误，返回-1
  6. print(re)
  7. print(re1)
  9.     运行结果：

6
-1

Process finished with exit code 0 

  1.     **三、列表操作**  
  4.     1. 切片
  6. lst = ["麻花藤", "王剑林", "马芸", "周鸿医", "向华强"]
  7. print(lst[0:3])  # ['麻花藤', '王剑林', '马芸']
  8. print(lst[:3])  # ['麻花藤', '王剑林', '马芸']
  9. print(lst[1::2])  # ['王剑林', '周鸿医'] 也有步长
  10. print(lst[2::-1])  # ['马芸', '王剑林', '麻花藤'] 也可以倒着取
  11. print(lst[-1:-3:-2])  # 倒着带步长
  13.     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

  1.     2. 删除pop()，remove()，clear()，del()的练习与区别。
  3. lst = ["麻花藤", "王剑林", "李嘉诚", "王富贵"]
  4. print(lst)
  5. deleted = lst.pop()  # 删除最后一个
  6. print("被删除的", deleted)
  7. print(lst)
  8. el = lst.pop(2)  # 删除2号元素
  9. print(el)
  10. print(lst)
  11. lst.remove("麻花藤")  # 删除指定元素
  12. print(lst)
  13. # lst.remove("哈哈") # 删除不存在的元素会报错
  14. # # print(lst)
  15. lst.clear()  # 清空list
  16. print(lst)
  17. # 切⽚删除，删除角标为1和2的元素
  18. del lst[1:3]
  19. print(lst)
  21.     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

  1.     3. 修改
  3. lst = ["Python", "Java", "Golang", "Perl", "JavaScript", "Node.js", "C#", "D"]
  5. # 修改
  6. lst[3] = "C++"
  7. print(lst)
  8. # 切片修改，步长为3,注意取值的个数
  9. lst[1:4:3] = ["VB"]
  10. print(lst)
  11. # 切片修改，步长为默认值1
  12. lst[1:4] = ["I like Python"]
  13. print(lst)
  15.       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 

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

Python
Java
Golang
Perl
JavaScript
Node.js
C#
D

Process finished with exit code 0

  1.     5. 其它操作  
  4.     reverse()：列表翻转
  6. lst = ["Python", "Java", "Golang", "Perl", "JavaScript", "Node.js", "C#", "D"]
  7. lst.reverse()
  8. print(lst)
  10.     运行结果：

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

Process finished with exit code 0

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