Develop Reference

Some functions from library works in python shell but not in a script

I'm having trouble getting certain functions from a library called art (https://github.com/sepandhaghighi/art) to run in a script, though they work fine in a shell. The script/commands entered sequentially look like this:
from art import *
randart() <(function fails in script, but succeeds in shell)
tart("test") <(different function, same library, succeeds in both shell and script)
import sys
print(sys.version)
The python version is 3.7.5 for both the shell and the script. The first function does not throw an error when run in a script, but does not give any output. Its desired output is a random ascii_art from a collection. I feel like I'm missing something really simple. Any ideas? The documentation on github reports "Some environments don't support all 1-Line arts", however they are the same python version on the same machine. Are there other portions of the environment that could be the cause?

You need to print randart() while writing in script. Make a habit of using print() for everything while printing. Shell is the place which returns the value by default whereas you need to tell the script window what to do with any name or function.
so use this:
from art import *
print(randart())

in the shell it is implicitly printed ... in a script you must explicitly
print(randart())

Why does the Python shell output something even when there is no "print" command?

I wrote the following code in Python IDLE, using its editor
import urllib.request
print(urllib.request.urlopen('https://github.com').read().decode('utf-8'))
and then saved the code as a script. After I ran the script, Python shell displayed the page source I want.
When I changed the above code to:
import urllib.request
urllib.request.urlopen('https://github.com').read().decode('utf-8')
and then ran the script, Python shell displayed nothing. This is understandable.
The weird thing for me, however, is that if I run the above code (the one without print) interactively in a Python shell, Python shell can still display the page source, as you see:
I don't understand why.
I use Python 3.6.3.

You are using the interactive python prompt. It automatically prints return values for you so that you can see the result of what you're doing.
Try typing 3 + 2. You know this doesn't print anything either - but you will see the result.
Likewise, if you put those two lines into a file you won't get any output.

It's because the shell is printing the result of execution. If you assign the function call to a variable then it will suppress the printing.
i.e. html = urllib.request.urlopen( ... )

Passing variables from Python GUI to PowerShell

So I am creating an application that can connect printers with a Python GUI that runs PowerShell scripts in the background. I was wondering if there was a way I could pass a variable inputted from a Python widget into a PowerShell script that is being invoked by Python. This variable would be the name of the printer that I could specify in Python so that I do not have to create separate scripts for each printer.
My code in Python that calls upon the PS script:
def connect():
if self.printerOpts.get() == 'Chosen Printer':
subprocess.call(["C:\\WINDOWS\\system32\\WindowsPowerShell\\v1.0\\powershell.exe",'-ExecutionPolicy','Unrestricted', '.\'./ScriptName\';'])
PS script that connects printer to computer:
Add-Printer -ConnectionName \\server\printer -AsJob
Basically, I am wondering if I can pass a variable from Python into the "printer" part of my PS script so that I do not have to create a different script for each printer that I would like to add.

A better way to do this would be completely in PowerShell or complete in Python.
What you're after is doable. You can pass it in the same way that you have passed -ExecutionPolicy Unrestricted, by ensuring that the PowerShell script is expecting the variable.
My Python is non-existant so please bear with if that part doesn't work.
Python
myPrinter # string variable in Python with printer name
subprocess.call(["C:\\WINDOWS\\system32\\WindowsPowerShell\\v1.0\\powershell.exe",'-ExecutionPolicy','Unrestricted', '.\'./ScriptName\';','-printer',myPrinter])
PowerShell
param(
$printer
)
Add-Printer -ConnectionName \\server\$printer -AsJob

The way that worked for me was first to specify that I was passing a variable as a string in my PS script:
param([string]$path)
Add-Printer -ConnectionName \\server\$path
My PS script was not expecting this variable. In my Python script I had to first define the my variable which named path as a string and then input "path" into the end of my subprocess function.
path = "c"
subprocess.call(["C:\\WINDOWS\\system32\\WindowsPowerShell\\v1.0\\powershell.exe",'-ExecutionPolicy','Unrestricted', 'Script.ps1', path])

set bash variable from python script

i'm calling a python script inside my bash script and I was wondering if there is a simple way to set my bash variables within my python script.
Example:
My bash script:
#!/bin/bash
someVar=""
python3 /some/folder/pythonScript.py
My python script:
anotherVar="HelloWorld"
Is there a way I can set my someVar to the value of anotherVar? I was thinking of printing properties in a file inside the python script and then read them from my bash script but maybe there is another way. Also I don't know and don't think it makes any difference but I can name both variable with the same name (someVar/someVar instead of someVar/anotherVar)

No, when you execute python, you start a new process, and every process has access only to their own memory. Imagine what would happen if a process could influence another processes memory! Even for parent/child processes like this, this would be a huge security problem.
You can make python print() something and use that, though:
#!/usr/bin/env python3
print('Hello!')
And in your shell script:
#!/usr/bin/env bash
someVar=$(python3 myscript.py)
echo "$someVar"
There are, of course, many others IPC techniques you could use, such as sockets, pipes, shared memory, etc... But without context, it's difficult to make a specific recommendation.

shlex.quote() in Python 3, or pipes.quote() in Python 2, can be used to generate code which can be evaled by the calling shell. Thus, if the following script:
#!/usr/bin/env python3
import sys, shlex
print('export foobar=%s' % (shlex.quote(sys.argv[1].upper())))
...is named setFoobar and invoked as:
eval "$(setFoobar argOne)"
...then the calling shell will have an environment variable set with the name foobar and the value argOne.

How to get Python interactive console in current namespace?

I would like to have my Python code start a Python interactive console (REPL) in the middle of running code using something like code.interact(). But the console that code.interact() starts doesn't see the variables in the current namespace. How do I do something like:
mystring="hello"
code.interact()
... and then in the interactive console that starts, I should be able to type mystring and get "hello". Is this possible? Do I need to set the "local" argument of code.interact() to something? What would this be set to? How should it be called?

Try:
code.interact(local=locals())

For debug I usually use this
from pdb import set_trace; set_trace()
it may help

Another way is to start the debugger, and then run interact:
import pdb
pdb.set_trace()
Then from the debugger:
(Pdb) help interact
interact
Start an interactive interpreter whose global namespace
contains all the (global and local) names found in the current scope.
(Pdb) interact
*interactive*
>>>

For Python 3.10.0:
code.InteractiveConsole(locals=locals()).interact()
See the Python documentation for more details.