[Python-Dev] PEP 370 and IronPython

[Christian Heimes]

Dear Pythonistas!

Michael Foord has written a blog posting [1] regarding IronPython, site
packages and my PEP 370. I'm referring to the section that talks about
an issue with PEP 370.

---
If you install CPython 2.6 on Windows it creates a folder in the
location: %APPDATA%\Python\Python26\site-packages. On my machine the
full path is:
C:\Users\michael\AppData\Roaming\Python\Python26\site-packages.

This is put on the path by site.py when you run Python and as it is a
user directory it doesn't require elevation to install there. You
install into the user directory rather than the 'usual' location with:

    python setup.py --user install

Herein lies another problem though. IronPython uses the standard Python
site.py, meaning that currently it shares the user site-packages folder
with CPython. This is not ideal as typically you will want separate
libraries install for IronPython. When Jython ports to Python 2.6 it
will have the same issue.
---

I didn't think about IronPython during the design phase of the PEP. I
didn't come into my mind that another implementation may require a
different site packages directory. After spinning my head around the
issue a simple solution came to me.

The solution requires a new attribute in the sys module that contains
the name of the implementation. As an alternative we could use the first
field of sys.subversion but I prefer an explicit attribute. I'm
proposing "sys.name" with a value of "CPython", "IronPython", "Jython"
or "PyPy". The site module uses the information of the attribute to
modify the path to the user site directory.

The altered user site directories are:

CPython:
  ~/.local/lib/python2.6/site-packages
  %APPDATA%/Python/Python26

IronPython:
  ~/.local/lib/ironpython2.6/site-packages
  %APPDATA%/Python/IronPython26

Jython:
  ~/.local/lib/jython2.6/site-packages
  %APPDATA%/Python/Jython26


Proposed patch:

Index: Lib/site.py
===================================================================
--- Lib/site.py (revision 75282)
+++ Lib/site.py (working copy)
@@ -74,7 +74,12 @@
 USER_SITE = None
 USER_BASE = None

+interpreter_name = getattr(sys, "name", "CPython")
+if interpreter_name == "CPython":
+    # b/w compatible name
+    interpreter_name = "python"

+
 def makepath(*paths):
     dir = os.path.abspath(os.path.join(*paths))
     return dir, os.path.normcase(dir)
@@ -253,10 +258,12 @@
         return USER_SITE

     if os.name == "nt":
-        USER_SITE = os.path.join(user_base, "Python" + sys.version[0] +
-                                 sys.version[2], "site-packages")
+        USER_SITE = os.path.join(user_base, interpreter_name.capitalize() +
+                                 sys.version[0] + sys.version[2],
+                                 "site-packages")
     else:
-        USER_SITE = os.path.join(user_base, "lib", "python" +
sys.version[:3],
+        USER_SITE = os.path.join(user_base, "lib",
+                                 interpreter_name.lower() +
sys.version[:3],
                                  "site-packages")

     return USER_SITE


The patch doesn't modify the search path for global directories. These
can be changed by altering sys.prefix and sys.exec_prefix.

Christian


[1]
http://ironpython-urls.blogspot.com/2009/10/distributing-ironpython-packages.html