Gracefully handling missing dependencies in bootstrap.py

[Erik Karulf]

I was using zc.buildout on a brand-new ubuntu machine when I was met with the following cryptic error message.

18:46 erik@fozzie % python bootstrap.py
Traceback (most recent call last):
  File "bootstrap.py", line 76, in <module>
    ws.find(pkg_resources.Requirement.parse('setuptools')).location
AttributeError: 'NoneType' object has no attribute 'location'
Exit 1

It turns out that I did not have the setuptools package installed.

Would it be possible to catch and display the error in a more graceful way?

try:
    import setuptools
except ImportError:
    print "setuptools dependency not satisfied."
    import sys
    sys.exit(1)

[Jim Fulton (jim-zope)]

On Fri, Aug 7, 2009 at 7:49 PM, Erik Karulf<email address hidden> wrote:
> Public bug reported:
>
> I was using zc.buildout on a brand-new ubuntu machine when I was met
> with the following cryptic error message.
>
> 18:46 erik@fozzie % python bootstrap.py
> Traceback (most recent call last):
>  File "bootstrap.py", line 76, in <module>
>    ws.find(pkg_resources.Requirement.parse('setuptools')).location
> AttributeError: 'NoneType' object has no attribute 'location'
> Exit 1
>
> It turns out that I did not have the setuptools package installed.
>
> Would it be possible to catch and display the error in a more graceful
> way?

My guess is that setuptools is installed, but without it's egg info.
Were you using the system Python?

Can you import pkg_resources?

In any case, I *can* an a check for this situation. I shouldn't have to, but ...

Jim

--
Jim Fulton

[Wichert Akkerman (wichert)]

I noticed the same thing on a clean Ubuntu 10.4 install today. This appears to be caused by Ubuntu installing pkg_resources but not the rest of setuptools, and all without any egg info.

A partial improvement apppears to be to try to import both pkg_resources and setuptools instead of just pkg_resources. That at least gets things to the point where zc.buildout downloads setuptools. It still fails later on though:

Downloading http://pypi.python.org/packages/2.6/s/setuptools/setuptools-0.6c11-py2.6.egg
Traceback (most recent call last):
  File "bootstrap.py", line 116, in <module>
    ws.find(pkg_resources.Requirement.parse(requirement)).location
AttributeError: 'NoneType' object has no attribute 'location'

Looking at it further the correct approach might be something like:

* if pkg_resources fails to import download & install setuptools
* if setuptools fails to import download & install setuptools
* if pkg_resources imports correctly but setuptools fails to import download & install setuptools and reload pkg_resources

I used the patch below as a quick test and that got things working for me, so it's probably a good start.

Index: bootstrap.py
===================================================================
--- bootstrap.py (revision 13408)
+++ bootstrap.py (working copy)
@@ -56,6 +56,7 @@
 to_reload = False
 try:
     import pkg_resources
+ import setuptools
     if not hasattr(pkg_resources, '_distribute'):
         to_reload = True
         raise ImportError
@@ -72,8 +73,10 @@

     if to_reload:
         reload(pkg_resources)
+ reload(setuptools)
     else:
- import pkg_resources
+ reload(pkg_resources)
+ import setuptools

 if sys.platform == 'win32':
     def quote(c):

[Wichert Akkerman (wichert)]

My initial patch was needlessly complicated, so I've attached a better version. There are two basic changes I have made:

* I try to import setuptools as well to make sure all of setuptools is available. This is required because Ubuntu defaults to only install pkg_resources.

* I always reload sys.modules('pkg_resources'). This is needed because ez['use_setuptools'](..) may import the wrong pkg_resources.