[Python learning notes] hello,python

to configure

Version: Python 3.7.6
Tool environment: Anaconda
Development tool: PyCharm
It's all free. It's good to find it on the Internet. It's right to choose the automatic installation path when installing. Don't be like I can't do it well so I often come back.

To open the command window, press [Win+R] - > Enter [cmd]

It's easy to use
Computer pdf reader: rice husk reader
pdf book download address: http://soshuvip.com/
Computer software installation official account: partner God

Try py (Interactive interpreter)

I still think it's more convenient and intuitive to use my own IDLE at the beginning.

  1. number
>>> 7/3
2.3333333333333335
>>> 7/1#Return floating point number forever
7.0
>>> 7//3 #Round down
2
>>> 5**2 #Exponential operation
25
>>> x=100 #Assignment not displayed
>>> 3*x
300
>>> 5+3j+2+2J #Complex number, J/j for imaginary part
(7+5j) 
  1. character string
>>> 'i\'m fine'
"i'm fine"
>>> print("hello\nworld")
hello
world
>>> print(r"hello\nworld")
hello\nworld
>>> print("hello\nworld")
hello
world
>>> print(r"hello\nworld")#r before quotation marks, restrict escape characters
hello\nworld
>>> print("""\
hello
world\
,python
""")#"Multiline characters, wrap each line automatically, \ \ restrict wrapping"
hello
world,python

>>> 3*"hello"+'py'
'hellohellohellopy'
>>> 'py''thon'
'python'
>>> x='py'
>>> x[0]#Indexes
'p'
>>> x[-1]#Negative number from right to left
'y'
>>> x+='thon'
>>> x[2:5]#section
'tho'
>>> x[:-2]+x[:1]
'pythp'
>>> x[100]#Beyond, baocuo
Traceback (most recent call last):
  File "<pyshell#24>", line 1, in <module>
    x[100]#Beyond, baocuo
IndexError: string index out of range
>>> x[:100]#Slice does not report error
'python'
>>> len(x)#Built in function len(), return length
6
  1. list
>>> fib=[1,1,2,3,5,8]
>>> fib
[1, 1, 2, 3, 5, 8]
>>> a=fib#Copy variable address
>>> a[0]=0
>>> fib[0:2]
[0, 1]
  1. Bitwise operator
>>> b=13#1101
>>> a=9#1001
>>> a&b#Bitwise and, 1001
9
>>> a|b#Bitwise OR, 1101
13
>>> a^b#Bitwise XOR, 0100
4
>>> ~a#Reverse by bit
-10
>>> a<<2#Shift, 100100
36
>>> True and False #and,or,not
False

In this case, the result of a=9(1001) reversed by bit is obviously (0110), which is not consistent with the example. Search for it, and write down the conclusion first: ~ n = -(n+1)
Similarly, c=-10,~c=-(-10+1)=9

Reference: understanding of the bit by bit negation operation in Python https://blog.csdn.net/strive_chuan/article/details/79242010

  1. Keyword is,in
>>> 5 in (1,2,3,5)#Determine whether it is included in the specified sequence
True
>>> 1 not in(1,2)
False
>>> a=1000
>>> id(a)#Built in function id(), return variable address
2301116519664
>>> b=1000
>>> id(b)
2301116519696
>>> a is b#Determine whether two identifiers refer to the same object
False
>>> a==b
True

There are some differences between "is" and "= =":
==The content is equal, and the address can be different;
is has the same content and address.

Reference: detailed explanation of the difference between is and = = in Python https://blog.csdn.net/qq_26442553/article/details/82195061

Tags: Python Anaconda Pycharm

Posted on Thu, 04 Jun 2020 12:45:06 -0400 by siddscool19