Manipulating dict

Let us understand how we can manipulate the dicts in Python.

  • We can add new key value pairs to dict by using typical assignment.

  • We can also use assignment operation to update existing key value pair in the dict.

  • setdefault can be used to get the element from the dict by using key. If key does not exist, it will update the dict with the key passed along with default value.

  • update can be used to merge a list of pairs (2 tuples) or a dict into the dict.

  • Elements from the dict can be removed using functions like pop and popitem.

    • pop is typically used to remove the element using key.

    • popitem is used to remove one of the item (typically last) from the dict.

d = {'id': 1, 'first_name': 'Scott', 'last_name': 'Tiger', 'amount': 1000.0}

d['commission_pct'] = 10 # Adding Element

d['phone_numbers'] = 1234567890

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': 10,
 'phone_numbers': 1234567890}

d['amount'] = 1500.0

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1500.0,
 'commission_pct': 10,
 'phone_numbers': 1234567890}

d = {'id': 1, 'first_name': 'Scott', 'last_name': 'Tiger', 'amount': 1000.0}

d.setdefault?

Docstring: D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D
Type:      builtin_function_or_method

d.setdefault('amount')

1000.0

d.setdefault('commission_pct')

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': None}

d = {'id': 1, 'first_name': 'Scott', 'last_name': 'Tiger', 'amount': 1000.0}

d

{'id': 1, 'first_name': 'Scott', 'last_name': 'Tiger', 'amount': 1000.0}

d.setdefault('commission_pct', 0)

0

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': 0}

d.setdefault('commission_pct', 100)

0

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': 0}

d.update?

Docstring:
D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
In either case, this is followed by: for k in F:  D[k] = F[k]
Type:      builtin_function_or_method

d = {'id': 1}

d

{'id': 1}

d.update({'first_name': 'Donald', 'last_name': 'Duck'})

d

{'id': 1, 'first_name': 'Donald', 'last_name': 'Duck'}

d.update([('amount', 1000.0), ('commission_pct', 10)])

d

{'id': 1,
 'first_name': 'Donald',
 'last_name': 'Duck',
 'amount': 1000.0,
 'commission_pct': 10}

d.update([('amount', 1500.0), ('commission_pct', 5), ('phone_numbers', 1234567890)])

d

{'id': 1,
 'first_name': 'Donald',
 'last_name': 'Duck',
 'amount': 1500.0,
 'commission_pct': 5,
 'phone_numbers': 1234567890}

d = {'id': 1, 'first_name': 'Scott', 'last_name': 'Tiger', 'amount': 1000.0}

d['commission_pct'] = 10 # Adding Element

d['phone_numbers'] = 1234567890

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': 10,
 'phone_numbers': 1234567890}

d.pop('phone_numbers')

1234567890

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': 10}

d.pop('phone_numbers') # throws KeyError

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-34-430dc980e4cd> in <module>
----> 1 d.pop('phone_numbers') # throws KeyError

KeyError: 'phone_numbers'

d.pop('phone_numbers', 'No such key exists')

'No such key exists'

d.pop?

Docstring:
D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
If key is not found, d is returned if given, otherwise KeyError is raised
Type:      builtin_function_or_method

d

{'id': 1,
 'first_name': 'Scott',
 'last_name': 'Tiger',
 'amount': 1000.0,
 'commission_pct': 10}

d.popitem?

Docstring:
D.popitem() -> (k, v), remove and return some (key, value) pair as a
2-tuple; but raise KeyError if D is empty.
Type:      builtin_function_or_method

d.popitem()

('commission_pct', 10)

d

{'id': 1, 'first_name': 'Scott', 'last_name': 'Tiger', 'amount': 1000.0}
Accessing Elements - dict Common Examples - dict