A 'KeyError' in Python occurs when trying to access a non-existent dictionary key. Common causes include typographical errors, case sensitivity, and dynamic key access. To prevent and handle 'KeyError', check if the key exists, use the 'get()' method, or utilize 'collections.defaultdict' for default values.

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UNDERSTANDING
‘KEYERROR’ IN
PYTHON

2. Introduction
A ‘KeyError’ is an exception in
Python that occurs when you try
to access a dictionary key that
does not exist. Dictionaries are
collections of key-value pairs,
and if you attempt to retrieve a
value using a key that is not in
the dictionary, Python raises a
‘KeyError’.

3. Common Causes
Trying to access a key that is not present in the dictionary.
Non-existent Key
Misspelling the key name.
Typographical Errors
Dictionary keys are case-sensitive, meaning ‘Key’ and ‘key’ are different.
Case Sensitivity
When keys are generated or retrieved from another source, they might not always
exist in the dictionary.
Dynamic Key Access

4. How to Prevent and
Handle ‘KeyError’
Check if Key Exists
Use the ‘get()’ Method
Default Values with ‘defaultdict’
Before accessing a key, check if it exists in the dictionary using the ‘in’
keyword.
Use the ‘get()’ method to retrieve a value; this method returns ‘None’ or a
specified default value if the key does not exist.
Use the ‘collections.defaultdict’ to provide default values for missing keys.

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