Python basic knowledge

A monster* 2021-08-09 16:31:52
python basic knowledge


python Reserved words

Reserved words are keywords , We can't use them as any identifier names .Python The standard library of provides a keyword modular , You can output all keywords of the current version :

>>> import keyword
>>> keyword.kwlist
['False', 'None', 'True', '__peg_parser__', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
>>>
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python notes

Single-line comments

# This is a single line comment .....
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Multiline comment

'''
Python It's an interpretative language : This means that there is no compilation in the development process . Be similar to PHP and Perl Language .
​
Python It's interactive language : It means , You can be in a Python Prompt >>> Then execute the code directly .
​
Python It's an object-oriented language : It means Python Support object-oriented style or code encapsulation in object programming technology .
'''
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python Indent

python The most distinctive feature is the use of indentation to represent code blocks , You don't need braces {} .

if True:
   print ("True")
else:
   print ("False")
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If Indents are inconsistent , Can cause a run error

if True:
   print("True")
else:
   print("False")
 print("False")
​
# File "C:/**/**/***/***.py", line **
# print("False")
^
# IndentationError: unindent does not match any outer indentation level
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python Multi line statement

If an expression / sentence For a long , We can use `` To implement multiline statements , Line feed display

total = val_1 + \
       val_2 + \
       val_3 - \
       val_4
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stay [], {}, or () Multiple lines in , No need to use backslash ``

stay In the dictionary {}

num_dict = {
   'num_1': 1,
   'num_2': 2,
   'num_3': 3
}
# print ---- {'num_1': 1, 'num_2': 2, 'num_3': 3}
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stay In the list []

num_list = [
1, 2, 3, 4,
   5, 6, 7, 8,
   9, 10, 11
]
# print ---- [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
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stay Tuple ()

num_tuple = (
1, 2, 3,
4, 5, 6,
7, 8, 9
)
# print ---- (1, 2, 3, 4, 5, 6, 7, 8, 9)
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python Show multiple statements on the same line

Use semicolons... Between statements ; Division

print(num_dict); print(num_tuple); print(num_list)
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python print Output and Output does not wrap

print('python print Output ')
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print The default output is line feed , If you want to implement no line wrapping, you need to add... At the end of the variable end=""

print( ' Hello ', end=" " )
print( 'python')
# Output ---->> Hello python
print( ' Hello ', end="*" )
print( 'python')
# Output ---->> Hello *ython
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python Multiple statements make up a code group

Indent the same set of statements into a block of code , We call it code group .

image if、while、def and class Such compound statements , The first line starts with keywords , With a colon (:) end , One or more lines of code following this line form a code group .

We call the first and subsequent code groups a clause (clause).

if val :
pass
elif val_2 :
pass
else :
pass
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python import And from...import

stay python use import perhaps from...import To import the corresponding module .

The whole module (somemodule) Import , The format is : import somemodule

Import a function from a module , The format is : from somemodule import somefunction

Import multiple functions from a module , The format is : from somemodule import firstfunc, secondfunc, thirdfunc

Import all functions in a module into , The format is : from somemodule import *

Import sys modular

import sys
for i in sys.argv:
print (i)
print ('\n python Path is ', sys.path)
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Import sys Modular argv,path member

# Import specific members
from sys import argv,path
# Because it has been imported path member , So there is no need to add sys.path
print('path:', path)
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