Dictionaries

Dictionary length, keyword in, and nested dictionaries

Learn how to use the `len` function and `in` keyword with dictionaries. Also, discover how to organize complex hierarchical data structures using nested dictionaries.

Let's create a new dictionary with some English-Portuguese translations:

translations = {
  'hello': 'olá',
  'please': 'por favor',
  'thank you': 'obrigado',
  'good morning': 'bom dia'
}

Python

We can use the English word as a key to find its translation:

translations = {
  'hello': 'olá',
  'please': 'por favor',
  'thank you': 'obrigado',
  'good morning': 'bom dia'
}
# get translation of 'good morning'
print(translations['good morning'])

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Output

Just like with strings, tuples, and lists, you can apply len() function to dictionaries.

len() will return the number of key-value pairs:

translations = {
  'hello': 'olá',
  'please': 'por favor',
  'thank you': 'obrigado',
  'good morning': 'bom dia'
}
# get number of key-value pairs
print(len(translations))

Python

Output

To check if a dictionary contains a specific key, use the in keyword.

Let's check if we have a translation for 'hi' and add it if necessary:

translations = {
  'hello': 'olá',
  'please': 'por favor',
  'thank you': 'obrigado',
  'good morning': 'bom dia'
}
# is key 'hi' in translations?
print('hi' in translations)
# add new key-value pair
translations['hi'] = 'Oi'
# check again
print('hi' in translations)

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Output

What will be the output?

my_dict = { 'a': 1, 'b': 2 }
print(len(my_dict))

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What will be the output?

my_dict = { 'a': (1,2,3), 'b': 2 }
print(len(my_dict))

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What will be the output?

my_dict = { 'a': (1,2,3), 'b': 2 }
print(2 in my_dict)

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What will be the output?

my_dict = { 'a': (1,2,3), 'b': 2 }
print('a' in my_dict)

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Sometimes you need to store more complex hierarchical data structures that cannot be represented by a single dictionary.

That's when we create dictionaries that contain other, nested dictionaries as their values.

Here's an example of such nested dictionaries:

student = {
  'name': 'John',
  'age': 16,
  'grades': {
    'math': 90,
    'science': 85,
    'history': 88
  }
}

Python

To access a value within the inner dictionary, we need to use multiple keys:

student = {
  'name': 'John',
  'age': 16,
  'grades': {
    'math': 90,
    'science': 85,
    'history': 88
  }
}
 
print(student['grades']['history'])

Python

Output

What will be the output?

my_dict = {
  'a': 1,
  'b': {
    'x': 90,
    'y': 80
  }
}
 
print(my_dict['b']['y'])

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What will be the output?

my_dict = {
  'a': 1,
  'b': {
    'x': 90,
    'y': 80
  }
}
 
print('x' in my_dict)

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What will be the output?

my_dict = {
  'a': 1,
  'b': {
    'x': 90,
    'y': 80
  }
}
 
print('x' in my_dict['b'])

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What will be the output?

my_dict = {
  'a': 1,
  'b': {
    'x': 90,
    'y': 80
  }
}
 
print(len(my_dict))

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What will be the output?

my_dict = {
  'a': 1,
  'b': {
    'x': 90,
    'y': 80
  }
}
 
print(len(my_dict['b']))

Python