python04

C:\Users\liuwe>python
Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 17:00:18) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> for i in range(3):
... print(i)
... else:
... print("无异常")
...
0
1
2
无异常
>>> for i in range(3):
... print(i)
... if i==1:
... break
... else:
... print("无break")
...
0
1
>>> while 1:
... print(1)
... break
... else:
... print("无break")
...
1

 

>>> n=3
>>> while n>=1:
... print(n)
... n=n-1
... else:
... print("无break")
...
3
2
1
无break

 

列表，元组和字典：数据结构：存数据的方式

增

>>> b=[1]
>>> type(b)
<class 'list'>
>>> a=[]
>>> a.append(1)
>>> a
[1]
>>> a.append(2)
>>> a
[1, 2]
>>> a.append("a")
>>> a
[1, 2, 'a']
>>> a.insert(0,"s")
>>> a
['s', 1, 2, 'a']
>>> a.append(2,"x")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: append() takes exactly one argument (2 given)
>>> a.insert(2,"x")
>>> a
['s', 1, 'x', 2, 'a']
>>>

>>> a.insert(2,"x")
>>> a
['s', 1, 'x', 2, 'a']
>>> a.extend(["m","n","z"])
>>> a
['s', 1, 'x', 2, 'a', 'm', 'n', 'z']
>>>

删

>>> del a[0]
>>> a
[1, 'x', 2, 'a', 'm', 'n', 'z']
>>>

改

>>> a[0]="ssss"
>>> a
['ssss', 1, 'x', 2, 'a', 'm', 'n', 'z']

 

a.remove()

a.pop()

 

 

查

 

列表，元组，字符串都是序列，使用坐标取值

>>> a=[1,2,3]
>>> for i in a:
... print(i)
...
1
2
3

当需要通过坐标实现计算过程使用如下方法
>>> for i in range(len(a)):
... print(a[i])
...
1
2
3
>>>

a=list(range(1,11))
>>> a
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> s=list("abcdef")
>>> a
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> s
['a', 'b', 'c', 'd', 'e', 'f']
>>> s[2]=1
>>> s
['a', 'b', 1, 'd', 'e', 'f']
>>> "".join(s)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: sequence item 2: expected str instance, int found
>>> s[2]="1"
>>> "".join(s)
'ab1def'
>>>

练习

1.一个list包含了2个a字母，请打印a字母所在的坐标

思考：用哪种方式可以获取坐标？if

l=[1,2,3,'a','a',4]

for i in  range(len(l)):

　　if l[i]=a"

　　　　print(i)

　　　　result.append(i)

print(result)

2.把两个a字母替换为“*”

l=[1,2,3,'a','a',4]

for i in  range(len(l)):

　　if l[i]=a"

　　　　print(i)

　　　　result.append(i)

print(result)

for i in result:

　　l[i]="*":

print(l)

3.构造一个list,包含字母和数字的，把全部的数字删除掉

方法1：过滤思想

result=[]

l=[1,2,3,'a','b','c']

for i in l:

　　if not  isinstance(i,(int,float,complex))：

　　　　result.append(i)

print(result)

 

方法2：原有方法基础上去改

result=[]

l=[1,2,3,'a','b','c']

for i in range(len(l)):

　　if isinstance(l[i],(int,float,complex)):

　　　　result.append(l[i])

for i in result:

　　l.remove(i)

print(l)

 

 

元组：元组的内容不能修改

a=(1,2)

for i in a : #基于值来进行遍历

　　print(i)

for i in  range(len(a)): #基于坐标的方法进行遍历

　　print(a[i])