print('Hello World!')
Hello World!
#2.2变量
message='Hello World!'
print(message)
Hello World!
message='Hello Python World!'
print(message)
Hello Python World!
#变量的命名和使用
#字母、数字（不能开头）、下划线
#不能包含空格
#python的关键字和函数名不能当作变量名
#2.3字符串
print('"Hello World!"')
print("'Hello World!'")
“Hello World!”
‘Hello World!’
#字符串标题大写
message='hello world!'
print(message.title())
Hello World!
#字符串大写
message='hello world!'
print(message.upper())
HELLO WORLD!
#字符串小写
message='HELLO WORLD!'
print(message.lower())
hello world!
#在字符串中使用变量
First='Hello'
Second='World'
Full=f'{
First} {
Second}'
print(Full)
Hello World
#使用制表符和换行符来添加空白
print('python')
print('\tpython')
python
python
print('python')
print('\npython')
python
python
print('python')
print('\\npython')
python
\npython
print('Languages:\nJAVA\nC\nPyhon')
Languages:
JAVA
C
Pyhon
print('Languages:\n\tJAVA\n\tC\n\tPyhon')
Languages:
JAVA
C
Pyhon
#删除空白
#rstrip()去除右边的空白
#lstrip()去除左边的空白
#strip()去除两边的空白
message=' python '
message.rstrip()
' python'
message=' python '
message.lstrip()
'python '
message=' python '
message.strip()
'python'
#引号问题
message="Python's strength"
print(message)
Python's strength
#数
#加减乘除
2+3
5
3-2
1
2*3
6
3/2
1.5
#浮点数
4/2
2.0
#乘方
3**2
9
3**3
27
10**5
100000
#多种运算
(2+3)*4
20
#整数和点数
4/2
2.0
1+2.0
3.0
2*3.0
6.0
#无论哪种运算，只要有操作数是浮点数，Python默认得到的总是浮点数
#数中的下划线
number=12_34
print(number)
1234
#同时给多个变量赋值
x,y,z=0,1,2
print(z)
2
#常量 常量一般为全大写
MAX_NUMBER=5000
#“#”为python注释，会被解释器忽略
import this
The Zen of Python, by Tim Peters
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!