Why To Use dict.get() method in Python Dictionary and Not just dict[] ?

<dict>.get(<key>) — VS — <dict>[<key>]

Pavol Kutaj

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Oct 28, 2021

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NOTES

• It allows you to provide a default value/expression if the key is missing
• …a sort of if/then mechanism without if statement

>>> d = {"name": "mr_paul"}
>>> d.get("name")
'mr_paul'
>>> d.get("job", print("seems to be unemployed"))
seems to be unemployed

• If omitted in the .get() , default_value is None, such that

>>> d.get("job", None)

• is the same as

>>> d.get("job")  # <-- No default specified -- defaults to None

• however, checking for a non-existent key with [] syntax throws an ERROR

>>> d["name"]
'mr_paul'
>>> d["job"]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'job'

'job'

• raises a KeyError which you can properly catch if needed

RETURN VALUE FOR NON-FOUND KEYS IN get()

• see Understanding .get() method in Python — Stack Overflow
• this counts words in a string

def count_words(doc):
    normalised_doc = "".join(c.lower() if c.isalpha() else " " for c in doc)
    frequencies = {}
    for word in normalised_doc.split():
        frequencies[word] = frequencies.get(word, 0) + 1
    return frequencies

• frequencies.get(word, 0) means that KeyError is never raised because of the use of get method
• and, the 0 is another optional parameter to be returned as a value if the key does not exist (the default is None )
• This is the primitive example combining these behaviors:

>>> d = {"name":"pavol"}
>>> d.get("age")>>> d.get("age",0)
0
>>> d["age"]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'age''age'