[Issues] Dictionary

Get Dictionary Items with Specified Initialization

dict.get(key, default = None))

returns the value of the item with the specified key.

Parameters

• key − This is the Key to be searched in the dictionary.
• default − This is the Value to be returned in case key does not exist.

See: Python dictionary get() Method

We can use dict.get(key, init_value) for initializing key-value pair in dictionary

E.g.: Counting how many times each element occurs in a list

 a = ["a", "b", "a", "a", "c", "c","a"]
 d = {}
 for el in a:
     d[el] = d.get(el, 0) + 1

d

 {'a': 4, 'b': 1, 'c': 2}

Remove Key from Python Dictionary

If you want to remove keys from Python dictionary, there’re different ways to do it:

• Use Python built-in del
• Use dict.pop()
• Use dictionary comprehension to create a new dictionary without the keys that need to be removed

Let’s say we have a dict like this:

person_info = {
    "name": "Ecko",
    "age": 20,
    "gender": "male"
}

and we want to remove the key age.

Built-in del

del person_info["age"]
print(person_info)

{'name': 'Ecko', 'gender': 'male'}

However, if the key doesn’t exist, del will raise an KeyError error. For example:

del person_info["address"]

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-14-8391b7d3a4c8> in <module>()
----> 1 del person_info["address"]

KeyError: 'address'

Therefore, we should check existence before removing:

key = "age"
if key in person_dict:
    del key

dict.pop()

To delete a key regardless of whether it is in the dictionary, use dict.pop()

pop(key[, default])

If key is in the dictionary, remove it and return its value, else return default. If default is not given and key is not in the dictionary, a KeyError is raised.

The advantage of this way is that you can get and delete an entry from a dict in one line of code. 👏

For example, we remove the existed key age:

age = person_info.pop("age")

print(age)
print(person_info)

We remove the key address which does NOT exist:

addr = person_info.pop("address", "earth")

print(addr)
print(person_info)

earth
{'name': 'Ecko', 'age': 20, 'gender': 'male'}

Use dictionary comprehension

{key:val for key, val in dict.items() if key != remove_key}

For our example:

{key:val for key,val in person_info.items() if key != "age"}

print(person_info)

{'gender': 'male', 'name': 'Ecko'}

Using dictionary comprehension, the a new dict will be created, and the original dict won’t be affected.

Reference

• How to remove a key from a Python dictionary?