Python: select dictionary items by key

You're checking the prefix the wrong way and you're not storing the result. You could use str.startswith and dict comprehension to generate the result:

>>> a = { ... 'car1': ('high cp', 'low fd', 'safe'), ... 'car2': ('med cp', 'med fd', 'safe'), ... 'car3': ('low cp', 'high fd', 'safe'), ... 'taxi1': ('high cp', 'low fd', 'safe', 'med wt'), ... 'taxi2': ('high cp', 'low fd', 'safe', 'high wt'), ... 'taxi3': ('high cp', 'low fd', 'safe', 'high wt') ... } >>> res = {k: v for k, v in a.items() if k.startswith('car')} >>> res {'car2': ('med cp', 'med fd', 'safe'), 'car3': ('low cp', 'high fd', 'safe'), 'car1': ('high cp', 'low fd', 'safe')} 

Instead of inserting a number to the format string your current check inserts the range object there which probably isn't the result you expect:

>>> 'car%s'% (range (4)) 'carrange(0, 4)' 

This works:

new_dict = {} for k in a.keys(): if 'car' in k: new_dict[k] = a[k] 

result:

>>new_dict {'car1': ('high cp', 'low fd', 'safe'), 'car2': ('med cp', 'med fd', 'safe'), 'car3': ('low cp', 'high fd', 'safe')} 

You never do anything with the keys you validate but print them. You need to add them to your new dictionary:

b ={} for key, val in a.items(): # .iteritems() for Python 2.x users if key == 'car%s' % (range (4)): b[key] = val print(b) 

Your code is would still be broken however. You need to make some changes:

• The only prefix you need to check is "car". Forget trying to match the whole string.

• This entire for loop could be made into a very simple dictionary comprehension:

  >>> a = { ... 'car1': ('high cp', 'low fd', 'safe'), ... 'car2': ('med cp', 'med fd', 'safe'), ... 'car3': ('low cp', 'high fd', 'safe'), ... 'taxi1': ('high cp', 'low fd', 'safe', 'med wt'), ... 'taxi2': ('high cp', 'low fd', 'safe', 'high wt'), ... 'taxi3': ('high cp', 'low fd', 'safe', 'high wt') ... } >>> {k: v for k, v in a.items() if k[0:3] == 'car'} {'car2': ('med cp', 'med fd', 'safe'), 'car3': ('low cp', 'high fd', 'safe'), 'car1': ('high cp', 'low fd', 'safe')} >>> 

what do you expect from range(4)? It returns [0, 1, 2, 3]

b = {} for key in range(4): new_key = "car%s" % key # generate new_key item = a.get(new_key) if item is not None: b[new_key] = item print (b) 

OR you want to get items only starts with car, read this link https://docs.python.org/3/library/stdtypes.html#str.startswith

b = {} for key, value in a.items(): if key.startswith("car"): b[key] = a[key] print (b) 

output

{'car2': ('med cp', 'med fd', 'safe'), 'car3': ('low cp', 'high fd', 'safe'), 'car1': ('high cp', 'low fd', 'safe')}