Dictionary

What is a dictionary in Python?

• A data structure that stores items in a sorted manner.

• A collection of elements arranged in a linear sequence.

• A collection of key-value pairs.

• A way to store only numeric values.

Answer explanation

A dictionary is a collection of keys and values. Dictionaries can not have duplicated items, meaning the keys are unique. A dictionary is defined using curly brackets {}. The key & value pair is defined using a colon (:) - key:value.

The syntax to define a dictionary:

dictionary_name = {key1:value1, key2:value2,...}

For example:

shopping_list = {"eggs":12 , "milk":2, "apples":5, "tomatoes": 6}

How do you create an empty dictionary in Python?

• my_dict = {}

• my_dict = []

• my_dict = ()

• my_dict = None

How do you access the value associated with a specific key in a dictionary?

• By using the index of the value.

• By using the value as an index.

• By using the key as an index.

• By using the value's position in the dictionary.

Answer explanation

You access the value associated with a specific key in a dictionary by using square brackets and placing the key inside the brackets. This allows you to retrieve the value (or data) that corresponds to that particular key.

Can a dictionary in Python contain duplicate keys?

• Yes, but only if the values are different.

• No, dictionaries cannot have duplicate keys.

• Yes, but it will cause an error when accessing values.

• Yes, but only if the keys are numbers.

Answer explanation

No, a dictionary in Python cannot contain duplicate keys. Each key in a dictionary must be unique. If you attempt to add a key that already exists in the dictionary, it will overwrite the existing key-value pair with the new value.

Remember that keys in a dictionary must be unique, and adding a key that already exists will simply update the associated value.

How do you add a new key-value pair to an existing dictionary?

• dictionary.add(key, value)

• dictionary.insert(key, value)

• dictionary[key] = value

• dictionary.append(key, value)

Answer explanation

You can add a new key-value pair to an existing dictionary by assigning a value to a new key using square brackets. If the key already exists, the assignment will update the value for that key; if it doesn't exist, a new key-value pair will be added to the dictionary.

What happens if you try to access a key that doesn't exist in a dictionary?

• Python raises an error.

• Python returns the value None.

• Python returns an empty string.

• Python returns a special "key not found" value.

Answer explanation

You will encounter a KeyError exception. This is because dictionaries in Python use keys to look up and retrieve values, and if the specified key is not found in the dictionary, Python raises a KeyError to indicate that the key does not exist.

How do you remove a key-value pair from a dictionary?

• dictionary.remove(key)

• del dictionary[key]

• dictionary.pop(key)

• dictionary.delete(key)

Answer explanation

The pop() method removes the item with the specified key name:

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict.pop("model")
print(thisdict)

The del keyword can also delete the dictionary completely.

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
del thisdict["model"]
print(thisdict)

The clear() method empties the dictionary:

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
thisdict.clear()
print(thisdict)

What does the len() function return when used with a dictionary?

• The number of key-value pairs in the dictionary.

• The sum of all the values in the dictionary.

• The length of the longest key in the dictionary.

• The number of keys in the dictionary.

Answer explanation

When you use the len() function with a dictionary in Python, it returns the number of key-value pairs (items) in the dictionary. In other words, it gives you the count of how many keys are present in the dictionary.

Can the values in a dictionary be of different data types?

• No, all values in a dictionary must be of the same data type.

• Yes, but only if they are numbers.

• Yes, values can be of different data types.

• Yes, but only if they are strings.

Answer explanation

In this example:

• The value associated with the "name" key is a string.

• The value associated with the "age" key is an integer.

• The value associated with the "city" key is a string.

• The value associated with the "scores" key is a list of integers.

• The value associated with the "is_student" key is a boolean.

• The value associated with the "info" key is another dictionary.

• The value associated with the "function" key is a lambda function.

This flexibility in data types makes dictionaries a powerful and versatile data structure for organizing and storing data in Python. You can mix and match data types within a dictionary to suit your specific needs.

How do you check if a key exists in a dictionary?

• Use the exist() method.

• Use the contains() method.

• Use the key_in() function.

• Use the 'in' keyword.

Answer explanation

Using the get() method:

You can also use the get() method, which allows you to specify a default value if the key is not found. If the key is present in the dictionary, get() returns its value; otherwise, it returns the default value. Here's an example:

my_dict = { "name": "John", "age": 30, "city": "New York" }

# Check if a key exists using get() age = my_dict.get("age")

if age is not None:

print(f"The 'age' key exists in the dictionary, and its value is {age}.")

else:

print("The 'age' key does not exist in the dictionary.")