Dynamically creating classes in python and __repr__

Question

This is a fairly straightforward question hopefully you all can enlighten me. In the example below how do I define __repr__ to be dynamically set to self.name?

Thanks all!

import re

inputlist = 'Project="Sparcy" Desc=""\nProject="Libs" Desc=""\nProject="Darwin" Desc=""\nProject="Aaple" Desc="The big project"'

regex = re.compile('([^ =]+) *= *("[^"]*"|[^ ]*)')

results = []
for project in inputlist.split("\n"):
    items = [ (k.strip(), v.strip()) for k, v in regex.findall(project)]
    if len(items) < 2:
        print("Houston we have a problem - Only %s k/v pair found for %s" % (len(items), project))
        continue
    item_dict = dict(items[1:])
    item_dict['name'] = items[0][1]
    klass = type(items[0][0], (object,), item_dict)
    results.append(klass)

print results

What I am looking for is this

psuedo code

for result in results
 type(result) → Project
 print result → Sparky

Answer 1

I'm guessing that you want

print results

to return

["Sparcy", "Libs", "Darwin", "Aaple"]

1. Printing a list shows the repr of its elements.
2. repr(elt) is determined by type(elt).__repr__.
3. Since in this case the elements are classes, you need to set the __repr__ for the type of the class.

---

import re

inputlist = '''\
Project="Sparcy" Desc=""
Project="Libs" Desc=""
Project="Darwin" Desc=""
Project="Aaple" Desc="The big project"
Site="Phoenix" Protocol="Cheese"'''

regex = re.compile('([^ =]+) *= *("[^"]*"|[^ ]*)')

results = []
for project in inputlist.split("\n"):
    items = [ (k.strip(), v.strip()) for k, v in regex.findall(project)]
    if len(items) < 2:
        print("Houston we have a problem - Only %s k/v pair found for %s" % (len(items), project))
        continue
    item_dict = dict(items[1:])
    item_dict['name'] = items[0][1]
    projectname=items[0][0]
    metametaklass=type('meta_'+projectname,(type,),{'__repr__':lambda cls: cls.__name__}) 
    metaklass=metametaklass(projectname,(type,),{'__repr__':lambda cls: cls.name})
    klass=metaklass(projectname+'_class', (object,), item_dict)
    results.append(klass)

print(results)

yields

["Sparcy", "Libs", "Darwin", "Aaple", "Phoenix"]

and

for result in results:
    print(type(result))
    print(result)    
    print('-'*80)

yields

Project
"Sparcy"
--------------------------------------------------------------------------------
Project
"Libs"
--------------------------------------------------------------------------------
Project
"Darwin"
--------------------------------------------------------------------------------
Project
"Aaple"
--------------------------------------------------------------------------------
Site
"Phoenix"
--------------------------------------------------------------------------------

PS. Note that this is a perversion of __repr__, since the repr of an object is supposed to be an unambiguous string representation of the object. That is, it is supposed to give enough information to reproduce the object. You probably should be defining a different print function instead of messing with metaclasses.