python学习笔记01

学习python已经有一段时间了，虽然会的不是太多，但也算有了一个好的开头，下面我把我所学的python基础总结一下。

文章目录变量和简单数据类型1.输出Hello World2.使用变量3.字符串3.1修改字符串大小写3.2合并字符串3.3使用制表符或换行符添加空白3.4删除空白4.数字5.避免类型错误6.注释列表1.一个简单的列表2.访问列表元素3.使用列表中的值4.修改列表中的元素5.列表中添加元素6.列表中插入元素7.列表中删除元素7.1del删除7.2pop()删除7.3remove()删除8.对列表排序8.1按字母顺序排序8.2按与字母顺序相反顺序排序8.3临时排序8.4倒序打印列表9.确定列表长度10.列表切片循环for循环while循环if判断语句if-elif-else结构
变量和简单数据类型
1.输出Hello World

这大概是所有初学者第一个学会的输出命令

>>> print("Hello World")
Hello World
>>>

>>> message="Hello World"
>>> print(message)
Hello World

注意变量名只能包含数字、字母和下划线，且只能用字母或下划线开头
变量名不能包含空格，但可使用下划线来分隔其中单词
不能将python关键字和函数名作为变量名
变量名应该既简短又具有描述性
慎重使用小写字母l和大写字母O，因为它们可能被人错看成数字1和0

3.字符串

在python中，用引号括起的都是字符串，其中的引号可以是单引号，也可以是双引号

>>> print("Hello World")
Hello World
>>> print('Hello World')
Hello World
>>>

首字母大写

>>> name='stefan'
>>> print(name.title())
Stefan
>>> name='stefan white'
>>> print(name.title())
Stefan White
>>>

全为大写、全为小写

>>> name='Stefan White'
>>> print(name.upper())
STEFAN WHITE
>>> name='STEFAN WHITE'
>>> print(name.lower())
stefan white
>>>

>>> first_str="my name is"
>>> last_str="stefan,and i like python"
>>> full_str=first_str+" "+last_str
>>> print(full_str)
my name is stefan,and i like python
>>>

>>> print('languages:npythonncnphpnjava')
languages:
python
c
php
java
>>>

分别删除字符串末尾、开头、两端的空白

>>> str=' python '
>>> str.rstrip()
' python'
>>> str.lstrip()
'python '
>>> str.strip()
'python'
>>>

这种删除是暂时的，要想永久删除如下

>>> str=' python '
>>> str=str.rstrip()
>>> str
' python'
>>>

如果字符串中有撇号 ‘ 的话，应使用双引号将字符串括起来

>>> str="i'm a student"
>>> print(str)
i'm a student
>>>

在终端会话和IDLE中，python直接返回运算结果

>>> 1+2
3
>>> 3-2
1
>>> 5*8
40
>>> 40*8
320
>>> 40/8
5.0
>>> 40%6
4
>>> 2*0.75
1.5
>>> 5.5/5
1.1
>>> 4.5+4.5
9.0
>>> 9.0-4.5
4.5
>>>

注意可能会出现这种情况，所有语言都存在这种情况，这是正常的

>>> 0.2+0.1
0.30000000000000004
>>> 3*0.1
0.30000000000000004
>>>

>>> age=18
>>> message="my age is "+age
Traceback (most recent call last):
  File "", line 1, in
    message="my age is "+age
TypeError: can only concatenate str (not "int") to str
>>>

这是因为age=18是整数(int)型变量，修改为如下

>>> age=18
>>> message="my age is "+str(age)
>>> print(message)
my age is 18

>>> #print("hello")这是一行注释
'''
a=1b=2c=3
'''
print("这是多行注释")

>>> words=['a','b','c','d']>>> print(words)
['a', 'b', 'c', 'd']>>>

>>> words=['a','b','c','d']>>> print(words)
['a', 'b', 'c', 'd']>>> print(words[0])
a
>>> print(words[2])
c
>>>

索引是从0开始而不是从1开始
最后一个列表元素指定索引为-1,倒数第二个为-2，以此类推

>>> print(words[-1])
d
>>> print(words[-2])
c
>>>

>>> words=['a','b','c','d']>>> print("The first word is "+words[0])
The first word is a
>>>

>>> words=['a','b','c','d']>>> words[0]='xwk'
>>> print(words)
['xwk', 'b', 'c', 'd']>>>

>>> words=['a','b','c','d']>>> words.append('e')
>>> words.append('f')
>>> words.append('g')
>>> print(words)
['a', 'b', 'c', 'd', 'e', 'f', 'g']>>>

使用insert()方法可在列表任意位置添加元素

>>> words=['a','b','c','d']>>> words.insert(0,'x')
>>> words.insert(2,'y')
>>> words.insert(4,'z')
>>> print(words)
['x', 'a', 'y', 'b', 'z', 'c', 'd']>>>

del可以删除任何位置的元素，前提是你知道它的索引

>>> words=['x', 'a', 'y', 'b', 'z', 'c', 'd']>>> del words[0]>>> words
['a', 'y', 'b', 'z', 'c', 'd']>>> del words[1]>>> words
['a', 'b', 'z', 'c', 'd']>>> del words[2]>>> words
['a', 'b', 'c', 'd']>>>

pop()删除列表末尾元素

>>> words=['a', 'b', 'c', 'd']>>> pop_words=words.pop()
>>> words
['a', 'b', 'c']>>> pop_words
'd'
>>>

显然，使用pop()删除元素，你可以得到被删除元素的值
你也可以使用它删除指定位置的元素

>>> words=['a', 'b', 'c', 'd']>>> pop_words=words.pop(2)
>>> words
['a', 'b', 'd']>>> print("the popped word is "+pop_words)
the popped word is c
>>>

如果你不知道要删除元素的索引，但知道它的值，你可以使用remove()删除

>>> words=['a', 'b', 'c', 'd']>>> words.remove('b')
>>> words
['a', 'c', 'd']>>>

>>> name=['stefan','jack','tom','demon','lily']>>> name.sort()
>>> print(name)
['demon', 'jack', 'lily', 'stefan', 'tom']>>>

>>> name=['stefan','jack','tom','demon','lily']>>> name.sort(reverse=True)
>>> print(name)
['tom', 'stefan', 'lily', 'jack', 'demon']>>>

以上两种方法永久改变列表顺序

8.3临时排序

>>> name=['stefan','jack','tom','demon','lily']>>> print(sorted(name))
['demon', 'jack', 'lily', 'stefan', 'tom']>>> print(name)
['stefan', 'jack', 'tom', 'demon', 'lily']>>>

列表顺序暂时改变

8.4倒序打印列表

>>> name=['stefan','jack','tom','demon','lily']>>> name.reverse()
>>> print(name)
['lily', 'demon', 'tom', 'jack', 'stefan']>>>

>>> name=['stefan','jack','tom','demon','lily']>>> len(name)
5
>>> words=['x', 'a', 'y', 'b', 'z', 'c', 'd']>>> len(words)
7
>>>

>>> name=['stefan','jack','tom','demon','lily']>>> name[0:4]['stefan', 'jack', 'tom', 'demon']>>> name[0:2]['stefan', 'jack']>>> name[0:]['stefan', 'jack', 'tom', 'demon', 'lily']>>> name[:-1]['stefan', 'jack', 'tom', 'demon']>>> name[-3:-1]['tom', 'demon']>>>

for i in range(1,5):
    print(i)
================================
1
2
3
4
>>>

words=['a','b','c','d']for word in words:
    print("the word is "+word)
================================================
the word is a
the word is b
the word is c
the word is d
>>>

sum=0
i=1
while i<=100:
    sum=sum+i
    i=i+1
print(sum)
================================
5050

a=1
b=1
c=2
str1='hello'
str2='world'
if a==b:
    print('a=b')
if a>=c:
    print('a>=c')
else:
    print('a<c')
if str1!=str2:
    print('str1!=str2')
else:
    print('str1=str2')
================================
a=b
a>>

age=12
if age<4:
    print("you need pay $0")
elif age<18:
    print("you need pay $5")
else:
    print("you need pay $10")
================================
you need pay $5

这篇就先写这么多，后面会继续总结更新

作者：北港不夏xwk