Single line notes #;

For multiline comments   Multiple # numbers' '' 'and' '' ';

python doesn't need parentheses, but pay attention to indentation and the use of spaces (it's best to separate every operator with spaces)

There are two ways to index characters: start with 0 from left to right and - 1 from right to left.

String interception method:   Variable [head subscript: tail subscript: step size]       What is not written represents the end or the end

+Is the connector of a string      * Copy current string

When there are escape characters in the content to be output   Add r before to represent the original string

>>> print('\n')       # Output blank line
>>> print(r'\n')      # Output \ n

Read a value input() from the keyboard   

x = input("Please enter a value:")
print(x)



Please enter a value:5
5

Use when there are multiple python statements on a line; separate

print will wrap automatically   Add end = "" "" at the end of the variable       No line breaks can be realized   End can be replaced with the desired operation

sep=""     Settable spacer

File -- file object to write

print("I won't wrap", end="")
print("I", "can't", "Line feed")
print("I", "can't", "Line feed", sep=".")
print("Backspace", end="\b")


output:
I won't wrap. I won't wrap
 I.can't.Line feed
 retreat

import and from     import module or function

Import the whole module in the format:   import somemodule

Import a function from a module in the following format:   from somemodule import somefunction

Import multiple functions from a module in the following format:   from somemodule import firstfunc, secondfunc, thirdfunc

Import all functions in a module in the following format:   from somemodule import *

multiline comment

a = b = c = 1
a, b, c = 1, 2, "char"

type(a)       You can view the object type of variable a

x = 2.11
print(type(x))


<class 'float'>

isinstance(a,int)     Judge whether a is of type int (bool belongs to int)

del x       Delete x object

del x,y,z     Delete the three objects x, y and Z

x /   y       Divide to get a floating point number

x // y     Divide to get an integer

x % y     Division remainder

x ** y     Power

x = 7; y = 2
print(x/y)
print(x // y)
print(x ** y)


3.5
3
49

A list is similar to a numeric value, but its elements support multiple types

list = [ 'abcd', 786 , 2.23, 'runoob', 70.2 ]

+No. connection list    * Copy list

If the third parameter is selected, the value is reversed

  Tuples are similar to lists   But its elements cannot be modified (can be spliced with +)   You can also index

tuple = ( 'abcd', 786 , 2.23, 'runoob', 70.2  )

tp = (0,) # an element, you need to add a comma after the element

Set     Used to test membership and delete duplicate elements

sites = {'Google', 'Taobao', 'Runoob', 'Facebook', 'Zhihu', 'Baidu', 'Runoob'}

# Output auto delete duplicate elements
{'Runoob', 'Facebook', 'Baidu', 'Zhihu', 'Taobao', 'Google'}

Creating an empty collection must use (), not {}     Such as sites()

# Member test
if 'Runoob' in sites :
    print('Runoob In collection')
else :
    print('Runoob Not in collection')


# Set can perform set operations
a = set('abracadabra')
b = set('alacazam')

print(a)

print(a - b)     # Difference sets of a and b

print(a | b)     # Union of a and b

print(a & b)     # Intersection of a and b

print(a ^ b)     # Elements in a and b that do not exist at the same time

Dictionary     Read by key

Mark with {}   Is a disordered     Keys: Values     Collection of

dictionary = {'one': 'aggregate', 'two': 'list', 'three': 'tuple', 'four': 'Dictionaries'}
print(dictionary)           # Output full dictionary
print(dictionary['one'], dictionary['two'])
print(dictionary.keys())      # Output all keys
print(dictionary.values())   # Output all values


#output
{'one': 'aggregate', 'two': 'list', 'three': 'tuple', 'four': 'Dictionaries'}
Collection list
dict_keys(['one', 'two', 'three', 'four'])
dict_values(['aggregate', 'list', 'tuple', 'Dictionaries'])

Create an empty dictionary with {}     Such as dictionary {}

Dictionary keywords cannot be duplicate and must be of immutable type

About functions of type conversion

int(x [.base])	Convert x to an integer
float(x)	Convert x to an integer
complex(real [, imag])	Create a complex number
str(x)	Will object × Convert to string
repr(x)	Will object × Convert to expression string
eval(str)	Used to evaluate a valid Python expression in a string and return an object
tuple(s)	Convert sequence s to a tuple
list(s)	Convert sequence s to a list
set(s)	Convert to variable set
dict(d)	Create a dictionary. d must be a (key, value) tuple sequence.
frozenset(s)	Convert to immutable set
chr(x)	Converts an integer to a character
ord(x)	Converts a character to its integer value
hex(x)	Converts an integer to a hexadecimal string
oct(x)	Converts an integer to an octal string