Loading functions from a file during run-time

[Bryant Huang]

Hello!

I would like to read in files, during run-time, which contain plain
Python function definitions, and then call those functions by their
string name. In other words, I'd like to read in arbitrary files with
function definitions, using a typical 'open()' call, but then have
those functions available for use.

The 'import' keyword is not appropriate, AFAIK, because I want to be
able to open any file, not one that I know ahead of time (and thus can
import at design-time).

I already have some code that I cobbled together from many newsgroup
posts, but I wonder if there's a cleaner/simpler way to do it.

The following is a toy example of what I'm doing so far. I have a file
called 'bar.txt' that contains two function definitions. I have a main
driver program called 'foo.py' which reads in 'bar.txt' (but should be
able to read any file it hasn't seen before), then calls the two
functions specified in 'bar.txt'.

= [bar.txt] =

def negate(x):
return -x

def square(x):
return x*x


= [foo.py] =

# open functions file
foo_file = open("bar.txt")
foo_lines = foo_file.readlines()
foo_file.close()
foo_str = "".join(foo_lines)

# compile code
foo_code = compile(foo_str, "", "exec")
foo_ns = {}
exec(foo_code) in foo_ns

# use functions
k = 5
print foo_ns["negate"](k)  // outputs -5
print foo_ns["square"](k)  // outputs 25


I'm not sure exactly what happens below the surface, but I'm guessing
the 'compile()' and 'exec()' commands load in 'negate()' and 'square()'
as functions in the global scope of 'foo.py'. I find that when I run
'compile()' and 'exec()' from within a function, say 'f()', the
functions I read in from 'bar.txt' are no longer accessible since they
are in global scope, and not in the scope of 'f()'.

Any pointers would be very welcome.

Thanks!
Bryant

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Re: Loading functions from a file during run-time

[Bryant Huang]

Ah, thanks a lot, Grant and Nick.

Let me try to clarify because I think I was unclear in specifying what
I want to do:

1. Read in a file containing a bunch of function definitions:

def f1(x):
  ...

def f2(x):
  ...

def f3(x):
  ...

def f4(x):
  ...

2. In wxPython, populate a CheckListBox with all the functions defined
in that file.

3. Allow the user to check some of the functions, say for example, f1()
and f3().

4. The program then executes f1() and f3() on some specified data.


The reason I asked these questions is because I don't know what
functions are contained in the function file ahead of time, but I still
want to be able to read those in, then based on which functions the
user selects, to run those accordingly, even though I still don't know,
at design-time, what functions are contained in the function file.

Does that make sense?

Thanks a lot!
Bryant

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Re: Loading functions from a file during run-time

[Bryant Huang]

Ah, thank you, Wensheng and T.J.! I have drawn bits and pieces from
what you have suggested. Both of your solutions work well.

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Re: Iteration within re.sub()?

[Bryant Huang]

Ah beautiful, thank you both, Robert and Mark, for your instant and
helpful responses. I understand, so the basic idea is to keep a
variable that is globally accessible and call an external function to
increment that variable...

Thanks!
Bryant

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Iteration within re.sub()?

[Bryant Huang]

Hi,

Is it possible to perform iteration within the re.sub() function call?

For example, if I have a string like:

str = "abbababbabbaaa"

and I want to replace all b's with an integer that increments from 0,
could I do that with re.sub()?

Replacing b's with 0's is trivial:

i = 0
pat = re.compile("b")
print pat.sub(`i`, str)

Now, how can I increment i in each replacement? Is this possible? Like,
using a lambda function, for example? Or do I use a different re
function altogether?

I use this trivial [ab]* language for simplicity, but I have a real
problem where I need to match a more complex regex and replace it with
an incrementing integer.

Thanks so much!
Bryant

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