Python基础之内置方法

Posted 2022-06-16 michealjy

目录

• 字符串的内置方法
  • 按索引取值
  • 切片(顾头不顾尾，步长)
  • 长度len
  • 成员运算
  • 移除两边空白strip
  • 切分split
  • 循环
  • lower&upper
  • startswith & endswith
  • replace
  • join
  • isdigit
• 列表类型的内置方法
  • 按索引取值（正反向取值同字符串）
  • 切片（同字符串）
  • 长度（同字符串）
  • 成员运算（同字符串）
  • 追加值
  • 删除
  • 循环(同字符串)
  • insert()
  • pop()
  • remove()
  • count()
  • index()
  • extend()
  • reverse()
  • sort()
• 字典类型内置方法
  • 按key取值：可存可取
  • 长度len(与字符串类似)
  • 成员运算(同字符串)
  • 删除
  • items()
  • 循环
  • get()
  • update()
  • setdefault()
  • 小练习

字符串的内置方法

按索引取值

msg = 'hello world'

print(f'msg[6]: msg[6]')
print(f'msg[-3]: msg[-3]')

msg[6]: w

msg[-3]: r

切片(顾头不顾尾，步长)

msg = 'hello nick'

print(f'msg[3:]: msg[3:]')
print(f'msg[3:8]: msg[3:8]')
print(f'msg[3:8:2]): msg[3:8:2]')
print(f'msg[3::2]: msg[3::2]')

print(f'切片所有：msg[:]')
print(f'反转所有 msg[::-1]: msg[::-1]')
print(f'切片-5~-2: msg[-5:-2:1]')
print(f'切片-2~-5: msg[-2:-5:-1]')

msg[3:]: lo nick msg[3:8]: lo ni msg[3:8:2]): l i msg[3::2]: l ik 切片所有：hello nick 反转所有 msg[::-1]: kcin olleh 切片-5~-2: ni 切片-2~-5: cin

长度len

msg = 'hello nick'

print(len(msg))

10

成员运算

msg = 'my name is micheal, micheal is handsome'

print(f"'nick' in msg: 'nick' in msg")
print(f"'jason' not in msg: 'jason' not in msg")
print(f"not 'jason' in msg: not 'jason' in msg") 

‘nick‘ in msg: False ‘jason‘ not in msg: True not ‘jason‘ in msg: True

移除两边空白strip

name = '&&&n ick'

print(f"name.strip('&'): name.strip('&')") #strip()默认为' ', 并且不修改原值，新创建空间
print(f'name: name')

#strip()应用场景
pwd = input('password: ') #用户可能会手抖输入空格
if pwd.strip() == '123':
    print('密码输入成功')

print(f"'*-& nick'.strip('*-& nick'): '*-& nick'.strip('*-& ')")

name.strip(‘&‘): n ick name: &&&n ick password: 123 密码输入成功 ‘*-& nick‘.strip(‘*-& nick‘): nick

切分split

info = "nick:male:19"
info_list1 = info.split(':')
info_list2 = info.split(':', 1)

print(f'info_list1:info_list1')
print(f'info_list2:info_list2')

info_list1:[‘nick‘, ‘male‘, ‘19‘] info_list2:[‘nick‘, ‘male:19‘]

循环

msg = 'hello nick'

for i in msg:
    print(i,end=' ')

h e l l o n i c k

lower&upper

name = 'Nick Chen'

print(f"name.upper(): name.upper()")
print(f"name.lower(): name.lower()")

name.upper(): NICK CHEN name.lower(): nick chen

startswith & endswith

name = 'Nick Chen'

print(f"name.startswith('Nick'): name.startswith('Nick')")
print(f'name.endswith('chen'): name.endswith('chen')')

name.startswith(‘Nick‘): True name.endswith(‘chen‘): False

replace

#str值replace()
name = 'nick shuai'

print(f"name.replace('shuai', 'handsome'): name.replace('shuai', 'handsome')")

name.replace(‘shuai‘, ‘handsome‘): nick handsome

join

lis = [1, 3, '13']
print(f"':'.join(lis): ':'.join(lis)") #报错，数字不可和字符串拼接

#str值join（）
lis = ['nick', 'male', '19']

print(f"':'.join(lis): ':'.join(lis)")

‘:‘.join(lis): nick:male:19

isdigit

#str之isdigit()应用场景

age = input('age: ')
if age.isdigit():
    age = int(age)
    
    if age < 18:
        print('小姐姐好')
    else:
        print('阿姨好’)
else:
    print(f'你的年龄能是这个age？')

age: 12 小姐姐好

列表类型的内置方法

按索引取值（正反向取值同字符串）

切片（同字符串）

长度（同字符串）

成员运算（同字符串）

追加值

# list之追加值
name_list = ['nick', 'jason', 'tank', 'sean']
name_list.append('tank sb')

print(f"name_list: name_list")

name_list: [‘nick‘, ‘jason‘, ‘tank‘, ‘sean‘, ‘tank sb‘]

删除

list之删除
name_list = ['nick', 'jason', 'tank', 'sean']
del name_list[2]

print(f"name_list: name_list")

name_list: [‘nick‘, ‘jason‘, ‘sean‘]

循环(同字符串)

insert()

#list之insert
name_list = ['nick', 'jason', 'tank', 'sean']
name_list.insert(1, 'handsome')

print(f'name_list: name_list')

name_list: [‘nick‘, ‘handsome‘, ‘jason‘, ‘tank‘, ‘sean‘]

pop()

#list之pop(),pop()默认删除最后一个元素
name_list = ['nick', 'jason', 'tank', 'sean']
print(f'name_list.pop(1): name_list.pop(1)')

name_list.pop(1): jason

remove()

# list之remove()
name_list = 'nick', 'jason', 'tank', 'sean'

print(f'name_list.remove("nick"): name_list.remove("nick")')

name_list.remove("nick"): None

count()

#list之count()
name_liat = ['nick', 'jason', 'tank', 'sean']

print(f"name_list.count('nick'): name_list.count('nick')")

name_list.count(‘nick‘): 1

index()

#list之index()
name_list = ['nick', 'jason', 'tank', 'sean']
print(f"name_list.index('nick'): name_list.index('nick')")

name_list.index(‘nick‘): 0

extend()

#list之extend
name_list = ['nick', 'jason', 'tank', 'sean']
name_list2 = ['nick handsome']
name_list.extend(name_list2)

print(f"name_list: name_list")

name_list: [‘nick‘, ‘jason‘, ‘tank‘, ‘sean‘, ‘nick handsome‘]

reverse()

#list之reverse()
name_list = ['nick', 'jason', 'tank', 'sean']
name_list.reverse()

print(f"name_list: name_list")

name_list: [‘sean‘, ‘tank‘, ‘jason‘, ‘nick‘]

sort()

#list之sort(), 使用sort列表的元素必须是同类型的
name_list = ['nick', 'jason', 'tank', 'sean']
name_list.sort()

print(f"name_list: name_list")

name_list.sort(reverse = True)
print(f"name_list_reverse: name_list")

name_list: [‘jason‘, ‘nick‘, ‘sean‘, ‘tank‘] name_list_reverse: [‘tank‘, ‘sean‘, ‘nick‘, ‘jason‘]

字典类型内置方法

按key取值：可存可取

#dict之按key取值
dic = 'a': 1, 'b': 2
print(f"first dic['a']: dic['a']")

dic['a'] = 3 #可以对原值进行修改
print(f"second dic['a']: dic['a']")

first dic[‘a‘]: 1 second dic[‘a‘]: 3

长度len(与字符串类似)

成员运算(同字符串)

删除

# dic之删除del
dic = 'a': 1, 'b': 2
del dic['a']

print(f"dic.get('a'): dic.get('a')")

# dic之删除pop
dic = 'a': 1, 'b': 2
dic.pop('a') #指定元素删除

print(f"dic.pop('a'):dic.pop('a')")
print(f"dic.pop('b'):dic.pop('b')")

dic.get(‘a‘): None

dic.get(‘a‘): None
dic.pop(‘b‘): 2

items()

dic = 'a': 1, 'b': 2

print(f"dic.items(): dic.items()")

dic = ‘a‘: 1, ‘b‘: 2print(f"dic.items(): dic.items()")

循环

# dic之循环
# dic是无序的，但是python3采用了底层优化算法，所以看起来是有序的，但是python2中的字典是无序

dic = 'a': 1, 'b': 2, 'c': 3, 'd': 4

for k, v in dic.items():# items可以换成keys()、values()
    print(k, v,end=' ')
    

dic = ‘a‘: 1, ‘b‘: 2, ‘c‘: 3, ‘d‘: 4for k, v in dic.items():# items可以换成keys()、values() print(k, v,end=‘ ‘)

get()

# dic之get()

dic = 'a': 1, 'b': 2

print(f"dic.get('a'): dic.get('a')")
print(f"dic.get('c'): dic.get('c')")

dic.get(‘a‘): 1
dic.get(‘c‘): None

update()

# dic之update()
dic1 = 'a': 1, 'b': 2
dic2 = 'c': 3
dic1.update(dic2)

print(f"dic1: dic1")

dic1: ‘a‘: 1, ‘b‘: 2, ‘c‘: 3

setdefault()

#dic之setdefault()  有指定key不会改变值，无指定key则改变值
dic = 'a': 1, 'b': 2

print(f"dic.setdefault('a'): dic.setdefault('a',3)")
print(f"dic: dic")
print(f"dic.setdefault('c'): dic.serdefault('c',3)")
print(f"dic: dic")

dic.setdefault(‘a‘): 1
dic: ‘a‘: 1, ‘b‘: 2
dic.setdefault(‘c‘): 3
dic: ‘a‘: 1, ‘b‘: 2, ‘c‘: 3

小练习

统计s = ‘hello tank tank say hello sb sb’中每个单词的个数

s = 'hello tank tank say hello sb sb'

s_split = s.split()
dic = dict()

for i in s:
    if i in dic:
        dic[i] += 1
    else:
        dic[i] = 1
print(dic)

‘hello‘: 2, ‘tank‘: 2, ‘say‘: 1, ‘sb‘: 2