Editing Python scripts with Python

Question

I'm trying to permanently edit variables within a Python script' source.

e.g.

urlpatterns = patterns('core.views',
)

to

urlpatterns = patterns('core.views',
    url(r'^admin/', include(admin.site.urls)),
)

e.g.

items = [
    'unicorn',
    'cats',
]

to

items = [
    'unicorn',
    'cats',
    'knights',
    'panthers',
]

The problem is capturing the single variable, extending it and replacing it, source of the python file can be quite big and varied.

This has probably been done already, but cannot seem to find much around.

Any ideas, tips or suggestions?

My solution for now:

I'm just going to add code at the bottom of the script file

e.g.

urlpatterns += patterns('core.views',
    url(r'^admin/', include(admin.site.urls)),
)

works for now :)

@radianthex: Your question is not at all clear. You say you are trying to do something but don't say what you tried or why it didn't work. Can you rephrase you question to make it more clear? — Bryan Oakley
– Bryan Oakley, Commented Apr 1, 2011 at 22:17
Are you trying to modify a python script using python? If so, why? It's easier to import it, extend it, and use that than it is to physically modify the source. — Daniel DiPaolo
– Daniel DiPaolo, Commented Apr 1, 2011 at 22:19
@Daniel: I know, but I need to make the changes within the source because it will be preferable for other people using the modules. — RadiantHex
– RadiantHex, Commented Apr 1, 2011 at 22:23
@RadiantHex if you are making permanent changes to Python source files on a regular basis, you should consider making your program more data-driven. Store relevant pieces in a database and dynamically do things at runtime. Modifying source files programmatically is a big code smell. — Daniel DiPaolo
– Daniel DiPaolo, Commented Apr 1, 2011 at 22:25
@Daniel: changes are a one time thing, basically the code needs to generate a set of files within a package based on a set of configurations. — RadiantHex
– RadiantHex, Commented Apr 1, 2011 at 22:27

ayanami · Accepted Answer · 2011-04-01 22:28:35Z

1

Python source code is, for this matter, a text file, so you pretty much open it and read/write data the usual way. I don’t think this is an amazingly good idea, but if you’re writing an installer of some sort...

answered Apr 1, 2011 at 22:28

ayanami

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Daniel DiPaolo · Accepted Answer · 2011-04-01 22:32:47Z

1

If you're generating from a template, you could use plain old string formatting:

tmpl = """import foo

bar = 12345

myList = [
    1,
    2,
    %s
]

otherStuff = %s"""

# figure out the values that need to go there

with f = open(filename, 'w+'):
    f.write(tmpl % (item1, item2))

(Alternately instead of hard-coding that string, you could read it in from a file as well)

Or you could use one of the many templating engines for Python.

answered Apr 1, 2011 at 22:32

Daniel DiPaolo

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1 Comment

RadiantHex Over a year ago

Thanks for the reply. I thought about this already, unfortunately I'm trying to support virtually as many scripts I can. Just lists/tuples would be fine.

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Editing Python scripts with Python

The problem is capturing the single variable, extending it and replacing it, source of the python file can be quite big and varied.

My solution for now:

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The problem is capturing the single variable, extending it and replacing it, source of the python file can be quite big and varied.

My solution for now:

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