For example, consider this simple dictionary:
If you try accessing its values by keys then see how it outputs:
>>> a_dict[1] 'Hello' >>> a_dict[3] 'Python' >>> a_dict[4] Traceback (most recent call last): File "<pyshell#3>", line 1, in <module> a_dict[4] KeyError: 4
As such, 1 and 3 keys exist, it displayed the respective values for those keys. The key 4 does not exist and an error generated KeyError: 4.
How can KeyError Python be avoided to crash a program?
The first way is using the try-except block and handling the KeyError there. You may display a descriptive message if KeyError occurs and the program will not crash.
Have a look at this example where KeyError is handled in try-except:
#A demo of avoding KeyError
a_dict = {1:'Hello',2:'World', 3:'Python'}
try:
print(a_dict[1])
print(a_dict[2])
print(a_dict[4])
except KeyError:
print("The key does not exist!")
Output:
In the output figure, you can see the values for the first two keys are displayed while key 4 produced an error that was handled in the except block.
A more practical example of KeyError
- In the following example, a small dictionary with only three items is created.
- The dictionary stores dummy phone numbers with names.
- The names act as the key while phone numbers as values.
- As you run the program, it will ask you to enter the name.
- If the name (key) exists in the dictionary, it will display the phone number, otherwise, except block will catch the KeyError and display a helpful message:
#A demo of KeyError with user input
Name = input("Enter a Name? ")
tel_dict = {'Hira': 485457454,'Shania': 789456123, 'Jimmy':69699696}
try:
print("The Telephone of ",Name ,":" ,tel_dict[Name])
except KeyError:
print("No Name exist!")
Sample outputs:
You see, if you have a large dictionary that requires some user input, you may handle the KeyError easily.
Second way – Using the get method of the dictionary
You may also manage the Python keyError exception by using the get method of the dictionary.
- The get method of the dictionary is used to return the value for the key.
- If a key does not exist the default is returned.
- If you do not provide the default, it defaults to None.
- That is why the KeyError is not raised as using the get method of the dictionary.
See an example below for learning how to use get method with default value:
#A demo of KeyError with Dictionary Get
emp_id = int(input("Enter Employee ID? "))
salary_dict = {1: '£3000',2: '£3500', 3: '£4000'}
sal = salary_dict.get(emp_id,'Wrong Employee ID!')
print("The Salary is: " ,sal)
In the output graphic, you can see the program displayed salaries for emp ID 1 and 3.
As I entered 5, it did not raise any exception (KeyError). Instead get method displayed the default message.
