Where does sys.path get replaced?

Question

Some library does change my sys.path in a way that I don't want it to.

But I can't find it. The affected virtualenv has a lot of libraries installed.

I replaced sys.path with a own class which alters the modifications, but this does not help, since the code seems to alter sys.path like this:

sys.path= [...] + sys.path

How can I find the "evil" code line and its stack trace?

Related

• Debugging modifications of sys.path

Committeewoman

Answer 1

I found the evil code line like this.

I alter sys.globals['sys'] in sitecustomize.py:

# sitecustomize.py
import sys

class AttributeIsReadonly(ValueError):
    pass

class MakeModuleAttributesReadonly(object):
    def __init__(self, module, readonly_attributes):
        self.module=module
        self.readonly_attributes=readonly_attributes

    def __setattr__(self, item, value):
        if item in ['module', 'readonly_attributes']:
            return super(MakeModuleAttributesReadonly, self).__setattr__(item, value)
        if item in self.readonly_attributes:
            raise AttributeIsReadonly('Access on attribute %r is readonly' % item)
        return setattr(self.module, item, value)

    def __getattr__(self, item):
        return getattr(self.module, item)

sys.modules['sys']=MakeModuleAttributesReadonly(sys, ['path'])

#import sys
#sys.path=sys.path # this will raise the above AttributeIsReadonly

It raises AttributeIsReadonly and I see the code line and the stack trace.

Committeewoman

Why didn't you just add this as an alternative answer to the existing question? – Apocrine

Since in the current question sys.path does not get modified. It is a different question. It's related but not the same. – Committeewoman

But surely having both answers in the same place would be more helpful for other users? Modification and replacement of the list are technically different, but you're solving the same underlying problem. Note that you could also have approached this by implementing __add__ in VerboseSysPath. – Apocrine

@Apocrine __add__ won't work if the modification gets done like this sys.path = [...] + sys.path. But thank you for the feedback, I will update the question. – Committeewoman

Yes, you'd need __radd__ etc. as well. I still don't see this as different enough to justify a separate question. – Apocrine

@jonrsharpe: having differently worded questions can be very helpful when searching for a problem. – Peaslee

@EthanFurman mainly if they're linked as duped to one canonical source of relevant information, though... – Apocrine