c++ - Should the order of import statements matter when importing a .so? -

i getting following import error when trying load python module compiled using boost python.

importerror: /path/to/library/libxml2.so.2: symbol gzopen64, version zlib_1.2.3.3 not defined in file libz.so.1 link time reference 

strangely don't see error if non standard module imported. i.e if import other module , module, fails import error. not sure what's going wrong or how debug.

edit: show issue:

$ python -c 'import json, libmyboost_py_lib' # not work!!! traceback (most recent call last):   file "<string>", line 1, in <module> importerror: path/to/xml_library/libxml2.so: symbol gzopen64, version zlib_1.2.3.3 not defined in file libz.so.1 link time reference $ python -c 'import libmyboost_py_lib, json' # works now!!! $ 

its not json, few other modules cause same issue when imported before module. eg. urllib2

the order of import statements matter.

as documented in python language reference:

once name of module known (unless otherwise specified, term “module” refer both packages , modules), searching module or package can begin. first place checked sys.modules, cache of modules have been imported previously. if module found there used in step (2) of import.

any module can change:

• sys.modules - cache of modules imported
• sys.path - search path modules

and can change import hooks well:

• sys.meta_path
• sys.path_hooks
• sys.path_importer_cache

the import hooks can provide ability load modules zip files, kind of archive files, network, etc.

---

import libmyboost_py_lib 

this statement going modify sys.modules sure, loading dependencies module cache. may modify sys.path too. common frameworks (e.g. boost, zope, django, requests...) ship batteries included / copy of modules depend on.

• django ships json
• requests ships urllib3

to see library load can use:

python -v -c 'import libmyboost_py_lib'