遍历
1. 遍历字典（只能遍历key值）
dic = {"1":21,"2":64,"3":98}
#遍历字典只是遍历key值
for c in dic:
print(c, end = ",")
结果：
1,2,3,
2. 遍历输出完整的字典内容
dic = {"1":21,"2":64,"3":98}
#遍历输出完整的key-value
for c in dic:
print(c,':',dic[c])
结果：
1 : 21
2 : 64
3 : 98
3. 输出字典内容的另一种方法
#遍历字典的内容
dict1 = {'abc':1,"cde":2,"d":4,"c":567,"d":"key1"}
for k,v in dict1.items():
print(k,":",v)
abc : 1
cde : 2
d : key1
c : 567
4. 遍历输出列表的序号和内容
#enumerate函数使用
sequence = [12, 34, 34, 23, 45, 76, 89]
for i, j in enumerate(sequence):
print(i, j)
0 12
1 34
2 34
3 23
4 45
5 76
6 89
5. 遍历多个列表，使用zip函数
#同时遍历两个或更多的序列，可以使用 zip() 组合,这个很有意思
questions = ['name', 'quest', 'favorite color']
answers1 = ['lancelot', 'the holy grail', 'blue']
answers2 = ["xiaoming","xiaobai","xiaolan"]
for q, a,h in zip(questions, answers1,answers2):
print('What is your {0}? It is {2}.'.format(q, a,h))
What is your name? It is xiaoming.
What is your quest? It is xiaobai.
What is your favorite color? It is xiaolan.
for q, a,h in zip(questions, answers1,answers2):
print('What is your {0}? It is {1}.'.format(q, a,h))#和上一个cell的区别在于引用的序号
What is your name? It is lancelot.
What is your quest? It is the holy grail.
What is your favorite color? It is blue.
6. 反向遍历
#反向遍历
for i in reversed(range(1, 10, 2)):
print(i)
9
7
5
3
1
文件的读写常用操作
f = open("aa.txt","w")
f.write("正在练习python。\n 认真学习")#f.write()写入内容
f.close()
区分f.read(),f.readline(),f.readlines()
f = open("aa.txt")
content = f.read()#f.read()将文件的全部内容读取并返回,返回的内容和文件一致
print(content)
f.close()
结果：
正在练习python。
认真学习
f = open("aa.txt","r")
#f.readline对文件进行逐行读取
content = f.readline()
content1 = f.readline()
print(content)
print(content1)
f.close()
正在练习python。
认真学习
f = open("aa.txt")
#f.readlines()返回文件内容的所有行，每一行作为列表的一个元素
content = f.readlines()
print(content)
f.close()
['正在练习python。\n', ' 认真学习']
