Python基础之内置方法

字符串的内置方法
列表类型的内置方法
字典类型内置方法

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': 2}print(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': 4}for 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}