Improve code: test for key in dict and store in datastore

Question

Hey, I'm fairly new to python I have this piece of code which stores the birth info to the datastore in Google App Engine. The code works but is it the correct way to do it? Is there a simpler way to do it, to make sure that the key exists before storing it in datastore?

def store_birthinfo(self, user, birthday):
  """
      Store birthinfo
  """

  name = ''
  date = ''
  place = ''
  country = ''

  for key in birthday.keys():
    if key == 'name':
      name = birthday['name']
    elif key == 'date':
      date = birthday['date']
    elif key == 'place':
      place = birthday['place']
    elif key == 'country':
      country = birthday['country']


  birthinfo = BirthInfo(user    = user,
                        date    = date,
                        place   = place,
                        country = country)
  birthinfo.put()

Answer 1

def store_birthinfo(self, user, birthday):
  """
      Store birthinfo
  """

  birthinfo = BirthInfo(user=user, **birthday)
  birthinfo.put()

see the docs on unpacking argument lists.

Answer 2

ʞɔıu's answer is the shortest, though it has slightly different semantics than yours, in that yours will provide an explicit empty string argument if the key is missing from the dictionary, while ʞɔıu's will omit the keyword argument altogether.

For the sake of completeness, there's a simpler way to do what you were doing without going all the way to **:

def store_birthinfo(self, user, birthday):
  """
      Store birthinfo
  """

  birthinfo = BirthInfo(user    = user,
                        date    = birthday.get('date', ''),
                        place   = birthday.get('place', ''),
                        country = birthday.get('country', ''))
  birthinfo.put()

Answer 3

A problem might be if your variable 'birthday' contains keys that the class BirthInfo doesn't expect. A more solid solution might be this which also gives you the clear insight into if blanks ones become None or empty string:

def store_birthinfo(self, user, birthday):
  data = dict(name='', date='', place='', country='')
  for key in [x for x in birthday.keys() if x in data]:
      data[key] = birthday[key]

  BirthInfo(user=user, **data).put()

Answer 4

You can create a default dictionary and then update the target dictionary as in

def store_birthinfo(self, user, birthday):
  """Store birthinfo"""
  birth_defaults = { 'name' : '',
                     'date' : '',
                     'place' : '',
                     'country' : ''}

  birth_defaults.update(birthday)
  birthinfo = BirthInfo(**birth_defaults)
  birthinfo.put()

In this way you will always have all the params set.

Answer 5

Building on Peter Bengtsson's post, you could also define the list of relevant keys, and leave data as an empty {} until the loop populates it.

def store_birthinfo(self, user, birthday):
    data = {}
    for key in 'date', 'place', 'country':
        data[key] = birthday.get(key, '')
    BirthInfo(user=user, **data).put()

I believe this is the most terse and extensible way to specify which keys to use from the birthday dict. With a little more verbosity, you could probably write a function to introspect BirthInfo for the arguments it can accept.