Get data of dictionaries

21 of october of 2024

Obtener datos de diccionarios

Disclaimer: This post has been translated to English using a machine translation model. Please, let me know if you find any mistakes.

Let's imagine that we have the following dictionary

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		dictionary = {
          "id": 1,
          "name": "John",
          "age": 30
      }
	
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If we want to obtain the value of the age, what is usually done is dictionary["age"]

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		dictionary = {
    "id": 1,
    "name": "John",
    "age": 30
}
dictionary["age"]
	
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>_ Output

But, what happens if the key we put in is not in the dictionary? Will it give us an error?

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		dictionary["country"]
	
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>_ Output

			
				---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[4], line 1
----> 1 dictionary["country"]
KeyError: 'country'

So if this happens in production, the program will crash

So to solve it we can use a try except to handle the error

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		try:
    dictionary["country"]
except KeyError:
    print("Key not found")
	
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>_ Output

			
				Key not found

But another solution to avoid filling the code with try except is to use the get method which allows us to obtain the value of a key and if it doesn't exist, it returns a default value.

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		dictionary.get("country", "Key not found")
	
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>_ Output

			
				'Key not found'

Another option is not to include the second option, in which case we get None if the key does not exist.

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		country = dictionary.get("country")
print(country)
	
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>_ Output

			
				None

Frequently asked questions

What's the difference between dictionary['key'] and dictionary.get('key') in Python?

dictionary["country"] raises a KeyError: 'country' if the key doesn't exist, which can crash the program in production. dictionary.get("country") never raises an exception: it returns None by default, or the default value you pass as the second argument — for example dictionary.get("country", "Key not found") returns the string 'Key not found' instead of failing.

How do I avoid a KeyError when accessing a missing dictionary key without using try/except?

Instead of wrapping every access in a try: dictionary["country"] except KeyError: print("Key not found") block, you can use the .get() method directly: dictionary.get("country", "Key not found") returns the given default value if the key is missing, avoiding repeated try/except blocks throughout the code.

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