interfacewithpython single line loops not recognizing outside environment

[jessdtate]

Description

When using single line loops in InterfaceWithPython, there is problem with using multiple variables. It works if the loop is self contained, ie, [ [i] for i,e in enumerate(V) if e != 0], but if it relies on another variable or imported package it doesn't recognize them, ie, [a[i] for i in b]. These all work in the python console. If the loop is expanded into long form, there are no problems. I suspect this problem and issues #1569 and #1570, are related.

Steps to Reproduce

1. add an interfacewithpython module
2. test the following code:
   V = [0, float('nan'), 500 ]
   print([ [i,e] for i,e in enumerate(V) if e != 0])
3. try these lines:
   import math
   print([i for i,e in enumerate(V) if math.isnan(e)])
   a = list(range(0,10))
   b = [1, 5, 6,8]
   print([ a[i] for i in b])

Expected behavior:

All these lines should work and the output should be:
[[1, nan], [2, 500]]
[1]
[1, 5, 6, 8]

Actual behavior:

returns an error, either 'math' not found, or 'a' not found

Versions

scirun v5.0-beta.F-37-gbc96c5d
os x 10.10 and 10.8

[dcwhite]

@jessdtate I can make the "math" error go away by importing math at the script level, so the functions are available automatically (like with the scirun API). Anymore very common modules I can import this way?

With the second error, you stumbled on a Python 3 list comprehension/variable scoping in closures/embedded shell/environment problem 😈 . Read these links for explanation (gory details included):

inducer/pudb#103 (open issue)
ipython/ipython#136 (open issue)
http://stackoverflow.com/questions/13905741/accessing-class-variables-from-a-list-comprehension-in-the-class-definition
http://stackoverflow.com/questions/20136955/python3-nested-list-comprehension-scope
http://stackoverflow.com/questions/22797782/scope-of-class-variable-with-list-comprehension

There are ugly workarounds where you have to define your own named function, like so:

a = list(range(0,10))
b = [1, 5, 6,8]
def aa(a, b):
	return [ a[i] for i in b]
aaa = aa(a,b)
print(aaa)

that does what you want. So I cannot solve this one myself, with the code you gave. I'm open to suggestions.

[jessdtate]

It may be a good idea to import the common modules. Since the expanded loop works too, it may not be worth fixing. It will probably work in a script too, I haven't tested that yet. Definitely needs to be documented at least.

[github-actions]

Stale issue message

[dcwhite]

@jessdtate Is this in the documentation?

[github-actions]

This issue is stale because it has been open 240 days with no activity. Remove the stale label or comment, or this will be closed in 60 days.