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We can utilize a conditional check to verify if our script is being run directly or being imported. Then we can handle those conditions differently based on our needs.
'__name__' is an special variable that holds the name of the program being executed.
We can use '__main__' to check if a script is running and gain more control over our programs
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Let's start by creating a new file
in our workspace called app.py.
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For our example here, I'll define the
symbol method that just prints a little
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hello statement from our app.
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And then call the method
to print that statement.
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We'll print
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Hello from app.
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Save our file.
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Go to the Console.
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And when we run our app, as expected,
we get our output., great.
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Let's create a second file,
we'll call it second_app.py.
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In here, we'll import app, And
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then we'll add another short print
statement, Well, from second app.
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We can save that, And run it.
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Let's see what happens
now with that import.
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Well, that's not entirely what we want.
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We really don't want to be calling
print hello just by importing app.py.
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This is where we can utilize that
conditional check with dunder name.
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Let's head back into app.py and add that.
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So right above our print_hello call,
We'll add,
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if __name__, == __main__.
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Come over here, indent.
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Now Python will check to see if app.py
is the main module being run, or
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if it is being imported.
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Let's double check this from
the command line to make sure
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things are working as we have intended.
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We run python app.py again.
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Nice, that still works.
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And if we run second_app.py,
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That's better.
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And since we've imported
app.py into second_app.py,
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we can call our print hello
function when and if we need it.
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App_print_hello,
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Save it.
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Let's clear our console here,
And run second_app.py again.
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Great, so we have access to
print hello from our second app.
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Let's take a quick peek at dunder name by
adding another print statement to app.py.
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Well print __name.
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Now, when we run our scripts,
we can see the value of dunder name,
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based on if the module is run directly or
imported.
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We'll run app.py and
see dunder_name is equal to dunder_main.
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And if we run second_app.py,
We see that dunder_name is equal to app.
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Notice here as well that by having
the print dunder_name statement in app.py
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outside of a function, that command
is run first inside second_app.py.
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This is another important reason to
have statements inside methods or
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inside a conditional check for
dunder name when using imports.
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Along your journey as a Pythonista, you'll
find many recommended best practices.
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This conditional check is a common
part of most Python programs and
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is used in all sorts
of Python applications
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from trade Python scripts to Python
frameworks like Flask and Django.
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With this best practice in place,
you can provide for
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better management with what
is happening in your scripts.
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I look forward to seeing what you build.
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Until next time, happy coding.
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