Python之一些容易被忽略的小细节（一）

- 日理万妓 2022-05-20 06:34 293阅读 0赞

**        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：

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：

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 found
    print(re)

运行结果：

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"]
    for el 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