Python dictionary keys() - How to get all keys from a dictionary

The Python dictionary has keys() method that returns all keys of it as a dict_keys object.

d = {'book': 24, 'pen': '5'}

keys = d.keys()

print(keys)  # dict_keys(['book', 'pen'])
print(type(keys))  # <class 'dict_keys'>

for k in keys:
    print(k)

# book
# pen

A dict_keys is an iterable, an object that can be iterated in the for loop. The following example shows how to get the dictionary keys as list.

d = {'book': 24, 'pen': '5'}

keys = d.keys()
a = list(keys)

print(keys)  # dict_keys(['book', 'pen'])
print(a)  # ['book', 'pen']

The relation of a dictionary and its keys

The dict_keys object is automatically updated by updating the dictionary. Its behavior is similar to the object referencing.

d = {'CA': 'California', 'NV': 'Nevada', 'TX': 'Texas'}

keys = d.keys()

d['VA'] = 'Virginia'

print(keys)  # dict_keys(['CA', 'NV', 'TX', 'VA'])

keys is the dictionary's keys and updated after updating the original dictionary.

Example

class User:

    def __init__(self, name):
        self.name = name


u = User(name='Josh')

d = u.__dict__
k = u.__dict__.keys()

print(d)  # {'name': 'Josh'}
print(k)  # dict_keys(['name'])

The __dict__ of an instance is the dictionary of properties. The instance's fields are the keys of its __dict__.

Keys and values

There are similar methods in Python dictionary, values() and items().

d = {'CA': 'California', 'NV': 'Nevada', 'TX': 'Texas'}

keys = d.keys()
values = d.values()
items = d.items()

print(keys)  # dict_keys(['CA', 'NV', 'TX'])
print(values)  # dict_values(['California', 'Nevada', 'Texas'])
print(items)  # dict_items([('CA', 'California'), ('NV', 'Nevada'), ('TX', 'Texas')])

keys() returns the dictionary's keys, values() returns its values, items() returns its pairs each of which is a tuple of a key and value.