python入门

python入门

>>> 2+2
4
>>> # This is a comment
... 2+2
4
>>> 2+2  # and a comment on the same line as code
4
>>> (50-5*6)/4
5.0
>>> 8/5 # Fractions aren't lost when dividing integers
1.6

To do integer division and get an integer result, discarding any fractional result, there is another operator,//:

 

[python]
>>> # Integer division returns the floor:  
... 7//3 
2 
>>> 7//-3 
-3 

>>> # Integer division returns the floor:
... 7//3
2
>>> 7//-3
-3

Complex numbers are also supported; imaginary numbers are written with a suffix ofj orJ. Complex numbers with a nonzero real component are written as(real+imagj), or can be created with thecomplex(real,imag) function.
 

[python]
>>> 1j * 1J 
(-1+0j) 
>>> 1j * complex(0, 1) 
(-1+0j) 
>>> 3+1j*3 
(3+3j) 
>>> (3+1j)*3 
(9+3j) 
>>> (1+2j)/(1+1j) 
(1.5+0.5j) 

>>> 1j * 1J
(-1+0j)
>>> 1j * complex(0, 1)
(-1+0j)
>>> 3+1j*3
(3+3j)
>>> (3+1j)*3
(9+3j)
>>> (1+2j)/(1+1j)
(1.5+0.5j)

To extract these parts from a complex number z, usez.real andz.imag.

[python]
>>> a=1.5+0.5j 
>>> a.real 
1.5 
>>> a.imag 
0.5 

>>> a=1.5+0.5j
>>> a.real
1.5
>>> a.imag
0.5

the last printed expression is assigned to the variable _

[python]
>>> tax = 12.5 / 100 
>>> price = 100.50 
>>> price * tax 
12.5625 
>>> price + _ 
113.0625 
>>> round(_, 2) 
113.06 

>>> tax = 12.5 / 100
>>> price = 100.50
>>> price * tax
12.5625
>>> price + _
113.0625
>>> round(_, 2)
113.06

2:Strings
[python]
>> 'spam eggs' 
'spam eggs' 
>>> 'doesn\'t' 
"doesn't" 
>>> "doesn't" 
"doesn't" 
>>> '"Yes," he said.' 
'"Yes," he said.' 
>>> "\"Yes,\" he said." 
'"Yes," he said.' 
>>> '"Isn\'t," she said.' 
'"Isn\'t," she said.' 

>>> 'spam eggs'
'spam eggs'
>>> 'doesn\'t'
"doesn't"
>>> "doesn't"
"doesn't"
>>> '"Yes," he said.'
'"Yes," he said.'
>>> "\"Yes,\" he said."
'"Yes," he said.'
>>> '"Isn\'t," she said.'
'"Isn\'t," she said.'
Continuation lines can be used, with a backslash as the last character on the line indicating that the next line is a logical continuation of the line:

[python]
>>> hello="this is not \n\ 
asdfasdf\n\ 
aksdfasd" 
>>> print(hello); 

>>> hello="this is not \n\
asdfasdf\n\
aksdfasd"
>>> print(hello);[python] view plaincopyprint?this is not  
asdfasdf 
aksdfasd 

this is not
asdfasdf
aksdfasd

a “raw” string:

[python]
>>> hello=r"this is not \n\ 
asdfasdf\n\ 
aksdfasd" 
>>> print(hello); 

>>> hello=r"this is not \n\
asdfasdf\n\
aksdfasd"
>>> print(hello);[python] view plaincopyprint?this is not \n\ 
asdfasdf\n\ 
aksdfasd 

this is not \n\
asdfasdf\n\
aksdfasd

Strings can be concatenated (glued together) with the + operator, and repeated with *:

[python]
>>> hello='Hello'; 
>>> world='World'; 
>>> hello=hello+world; 
>>> hello 
'HelloWorld' 

>>> hello='Hello';
>>> world='World';
>>> hello=hello+world;
>>> hello
'HelloWorld'[python] view plaincopyprint?>>> '<'+hello*5+'>' 
'<HelloWorldHelloWorldHelloWorldHelloWorldHelloWorld>' 

>>> '<'+hello*5+'>'
'<HelloWorldHelloWorldHelloWorldHelloWorldHelloWorld>'