How to access a variable in IPython from a program executed by %run

Question

I have a program like this:

if __name__=="__main__":
  foo = expensiveDataProcessClass(filepath)

  y = foo.doStuff()
  y = foo.doOtherStuff()

I'm testing things out as a I build it in ipython with the %run myprogram command.

After it's running, since it takes forever, I'll break it with ctrl+C and go rewrite some stuff in the file.

Even after I break it, though, IPython has foo stored.

>type(foo) 
__main__.expensiveDataProcessClass

I'm never having to edit anything in foo, so it would be cool if I could update my program to first check for the existence of this foo variable and just continue to use it in IPython rather than doing the whole creation process again.

aruisdante · Accepted Answer · 2015-02-27 23:31:23Z

1

You could first check for the variable's existence, and only assign to it if it doesn't exist. Example:

if __name__=="__main__":
    if not "foo" in globals()
        foo = expensiveDataProcessClass(filepath)

However, this won't actually work (in the sense of saving a foo assignment). If you read IPython's doc on the %run magic, it clearly states that the executed program is run in its own namespace, and only after program execution are its globals loaded into IPython's interactive namespace. Every time you use %run it will always not have foo defined from the program's prospective.

edited Feb 27, 2015 at 23:31

answered Feb 27, 2015 at 23:17

aruisdante

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3 Comments

Tyler Wood Over a year ago

So this would work in normal execution, just not with ipython's %run?

aruisdante Over a year ago

If you mean by doing python myscript.py then no, because python programs are always given a fresh execution environment. In fact %run is, from any program's prospective, exactly the same as executing it normally. The difference is the final program state is then loaded into IPython for you to examine. This is useful for debugging purposes to see what state things where in when it went wrong.

Thomas K Over a year ago

However, %run -i runs a script in your interactive namespace - so then this check would would work.

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