what are the various ways to handle the error in dictionary(python)?Also input the values from the user.
Answers
Answer:
Explanation:
A Python KeyError exception is what is raised when you try to access a key that isn’t in a dictionary (dict).
Python’s official documentation says that the KeyError is raised when a mapping key is accessed and isn’t found in the mapping. A mapping is a data structure that maps one set of values to another. The most common mapping in Python is the dictionary.
The Python KeyError is a type of LookupError exception and denotes that there was an issue retrieving the key you were looking for. When you see a KeyError, the semantic meaning is that the key being looked for could not be found.
In the example below, you can see a dictionary (ages) defined with the ages of three people. When you try to access a key that is not in the dictionary, a KeyError is raised:
>>> ages = {'Jim': 30, 'Pam': 28, 'Kevin': 33}
>>> ages['Michael']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 'Michael'
Here, attempting to access the key 'Michael' in the ages dictionary results in a KeyError being raised. At the bottom of the traceback, you get the relevant information:
The fact that a KeyError was raised
The key that couldn’t be found, which was 'Michael'
The second-to-last line tells you which line raised the exception. This information is more helpful when you execute Python code from a file.
Note: When an exception is raised in Python, it is done with a traceback. The traceback gives you all the relevant information to be able to determine why the exception was raised and what caused it.
Learning how to read a Python traceback and understanding what it is telling you is crucial to improving as a Python programmer. To learn more on Python tracebacks, check out Understanding the Python Traceback
In the program below, you can see the ages dictionary defined again. This time, you will be prompted to provide the name of the person to retrieve the age for:
# ages.py
ages = {'Jim': 30, 'Pam': 28, 'Kevin': 33}
person = input('Get age for: ')
print(f'{person} is {ages[person]} years old.')
This code will take the name that you provide at the prompt and attempt to retrieve the age for that person. Whatever you type in at the prompt will be used as the key to the ages dictionary, on line 4.
Repeating the failed example from above, we get another traceback, this time with information about the line in the file that the KeyError is raised from:
$ python ages.py
Get age for: Michael
Traceback (most recent call last):
File "ages.py", line 4, in <module>
print(f'{person} is {ages[person]} years old.')
KeyError: 'Michael'
The program fails when you give a key that is not in the dictionary. Here, the traceback’s last few lines point to the problem. File "ages.py", line 4, in <module> tells you which line of which file raised the resulting KeyError exception. Then you are shown that line. Finally, the KeyError exception provides the missing key.
So you can see that the KeyError traceback’s final line doesn’t give you enough information on its own, but the lines before it can get you a lot closer to understanding what went wrong.
Note: Like the example above, most of the other examples in this tutorial make use of f-strings, which were introduced in Python 3.6.
Where Else You Might See a Python KeyError in the Standard Library
The large majority of the time, a Python KeyError is raised because a key is not found in a dictionary or a dictionary subclass (such as os.environ).
In rare cases, you may also see it raised in other places in Python’s Standard Library, such as in the zipfile module, if an item is not found in a ZIP archive. However, these places keep the same semantic meaning of the Python KeyError, which is not finding the key requested.
In the following example, you can see using the zipfile.ZipFile class to extract information about a ZIP archive using .getinfo():