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====== Python ======

===== Passing Variables =====

* Python will not change what I think are global variables in functions.
  * If, for example, you have a variable xyzzy, and you reference it in a function, python creates a new one.
  * So you have to pass in xyzzy if you want to modify it.
  * You then have to return it explicitly, because Python returns the value of the last expression.
<code>
    def incrementXyzzy():
       xyzzy = xyzzy + 1
    #does not work because xyzzy is a local created on the fly   
</code>

<code>
    def incrementXyzzy(xyzzy):
       xyzzy = xyzzy + 1
    #xyzzy is passed in and can be incremented. it will be returned   
</code>

<code>
    def incrementXyzzy(xyzzy):
       xyzzy = xyzzy + 1
    return xyzzy   #explict return is better
    #xyzzy is passed in and can be incremented. it will be returned   
</code>

<code>
     xyzzy = incrementXyzzy(xyzzy):

#the calling function **must** assign the returned value   
</code>

===== Read Csv =====

* import csv
  * file = open('Emp_Info.csv', 'r')
  * try:
  * reader = csv.reader(file)
  * for each_row in reader:
  * print(each_row)
  * finally:
  * file.close()

===== Lists =====

* create list - stock = []
  * append to list - stock.append("fred")

===== Pip =====

* python -m pip install somePackage
  * sudo python -m pip install email_to <------------------- does not work
error: externally-managed-environment

This environment is externally managed
To install Python packages system-wide, try apt install
python3-xyz, where xyz is the package you are trying to install.
    
If you wish to install a non-Debian-packaged Python package, create a virtual environment using python3 -m venv path/to/venv.

Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make     sure you have python3-full installed.
    
For more information visit http://rptl.io/venv

===== Files =====

* open file - input = ("someFileLocation", "r")
  * read a line - line = input.readline()

<code>
file_path = 'randomfile.txt'
file_text = open(file_path, "r")
a = True
while a:
    file_line = file_text.readline()
    if not file_line:
        print("End Of File")
        a = False
file_text.close()
</code>

<code>
file = open("randomfile.txt", "r")

while (f := file.read()):
    process(f)

file.close()
</code>

==== Packages ====

* packages live in C:\Users\Donald\AppData\Local\Programs\Python\Python313\Lib\site-packages
  * a pip install of exifread appeared to work but did not create this package in the above directory
  * found it on Git, downloaded a zip, and copied the package to the site-packages directory

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