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hannah dong

admin 11月 13, 2020 0

Introduction to Python - Lesson 1

The reason why I learn Python is to prepare for Machine Learning.

Quick Start

Download Python

Download here if you haven’t yet.

Check if you have already downloaded Python

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$ python --version

If the terminal displays as below, you have already downloaded it; Otherwise you haven’t.

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Python 2.7.10

Run a Python File

Create a folder

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$ mkdir python

Make a file

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$ >hello.py

Edit hello.py

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$ vi hello.py

Enter “i” and input the following

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# Define a main() function that prints a little greeting
def main():
  print "Hello Alice"
# This is the standard boilerplate that calls the main() function.
if __name__ == '__main__':
  main()

Press esc, then input “:x” to exit
Input

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python hello.py

The result is

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Hello Alice

The above example shows how to make a basic python file, then we will see how to use the existing functions within Python, rewrite hello.py as following

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import sys
def Hello(name):
  name = name + '!!!'
  print 'Hello', name
# Define a main() function that prints a little greeting
def main():
  Hello(sys.argv[1])
# This is the standard boilerplate that calls the main() function.
if __name__ == '__main__':
  main()

Press esc, then input “:x” to exit
Input 

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python hello.py Alice

The result is

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Hello Alice!!!

The above example shows how to make inputs through command line, then we will see how to use if/else function, rewrite hello.py as following

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import sys
def Hello(name):
  if name == 'Alice' or name == 'Nick':
    name = name + '???'
  else:
    name = name + '%%%'
  name = name + '!!!'
  print 'Hello', name
# Define a main() function that prints a little greeting
def main():
  Hello(sys.argv[1])
# This is the standard boilerplate that calls the main() function.
if __name__ == '__main__':
  main()

Press esc, then input “:x” to exit
Input 

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python hello.py Alice

The result is

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Hello Alice???!!!

Run Python Command

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$ python

The usage of ‘’ and “”

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>>> "I "love" this exercise"
>>> 'I "love" this exercise'
>>> "isn't"
>>> "isn't"
>>>

Press cmd+d to exit

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>>> help(sys)

Long press q to exit

This is the first day I learned Python, keep going!

Reference here

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