• When debugging in PHP, we frequently find it useful to simply stick a var_dump() in our code to show me what a variable is, what its value is, and the same for anything that it contains.
  • What is a good Python equivalent for this?

When debugging in PHP, we frequently find it useful to simply stick a var_dump() in our code to show me what a variable is, what its value is, and the same for anything that it contains.

  • To display a value, you can use the pprint module. The easiest way to dump all variables with it is to do
python code 
import pprint

pprint.pprint(globals())
pprint.pprint(locals())
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  • If you are running in CGI, a useful debugging feature is the cgitb module, which displays the value of local variables as part of the traceback.

Python code 
def dump(obj):
  '''return a printable representation of an object for debugging'''
  newobj=obj
  if '__dict__' in dir(obj):
    newobj=obj.__dict__
    if ' object at ' in str(obj) and not newobj.has_key('__type__'):
      newobj['__type__']=str(obj)
    for attr in newobj:
      newobj[attr]=dump(newobj[attr])
  return newobj
  • Here is the usage
Python code 
class stdClass(object): pass
obj=stdClass()
obj.int=1
obj.tup=(1,2,3,4)
obj.dict={'a':1,'b':2, 'c':3, 'more':{'z':26,'y':25}}
obj.list=[1,2,3,'a','b','c',[1,2,3,4]]
obj.subObj=stdClass()
obj.subObj.value='foobar'
from pprint import pprint
pprint(dump(obj))

and the results

Python code 
{
'__type__': '<__main__.stdClass object at 0x2b126000b890>',
 'dict': {'a': 1, 'c': 3, 'b': 2, 'more': {'y': 25, 'z': 26}},
 'int': 1,
 'list': [1, 2, 3, 'a', 'b', 'c', [1, 2, 3, 4]],
 'subObj': {'__type__': '<__main__.stdClass object at 0x2b126000b8d0>',
            'value': 'foobar'},
 'tup': (1, 2, 3, 4)
}
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  • You can simply install it using pip:
Python code 
pip install var_dump

  • Here we use self-written Printer class, but dir() is also good for outputting the instance fields/values.

class Printer:

Python code 
       def __init__ (self, PrintableClass):
           for name in dir(PrintableClass):
               value = getattr(PrintableClass,name)
               if  '_' not in str(name).join(str(value)):
                    print '  .%s: %r' % (name, value)
  • The sample of usage:
Python code 
Printer(MyClass)

  • In PHP’s var_dump() is pprint() with the getmembers() function in the built-in inspect module:
python code 
from inspect import getmembers
from pprint import pprint
pprint(getmembers(yourObj))

  • The best equivalent to PHP’s var_dump($foo, $bar) is combine print with vars:
python code 
print vars(foo),vars(bar)
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