Dictionaries in Python, What is Python Dictionary?, Data Structures in Python, Create a Dictionary, and Python Dictionary Methods.
A useful data type built into Python is the dictionary. Dictionaries are sometimes found in other languages as “associative memories” or “associative arrays”. Unlike sequences, which are indexed by a range of numbers, dictionaries are indexed by keys, which can be any immutable type; strings and numbers can always be keys.
Python Data Structures – Dictionaries
1. Accessing Dictionary Items
2. Change a Values
3. Print a Dictionary
4. Check if a Key Exists
5. Find Dictionary Length
6. Adding Items to a Dictionary
7. Removing Items
8. Copy a Dictionary
9. Nested Dictionaries
10. The dict() Constructor
What is Dictionary?
A dictionary is a collection that is unordered, changeable, and indexed. In Python, dictionaries are written with curly brackets, and they have keys and values.
Example:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
print(man )
Operations on Dictionaries
1. Accessing Dictionary Items
We can access the items of a dictionary by referring to its key name, inside square brackets:
Example:
Get the value of the “age” key:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
x = man[“age”]
print (x)
2. Change Values
We can change the value of a specific item by referring to its key name:
Example:
Change the “age” to 45:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
man [“age”] = 45
print(man)
3. Print Dictionary
a. Print all (key and value pairs)
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
print(man)
b. Print Keys
Print all key names in the dictionary, one by one:
for x in man:
print(x)
c. Print Values
Print all values in the dictionary, one by one:
for x in man:
print(man[x])
or
for x in man.values():
print(x)
d. Loop through both keys and values, by using the items() function:
for x, y in man.items():
print(x, y)
4. Check if Key Exists
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
if “name” in man:
print(“Yes, ‘name’ is one of the keys in the man dictionary”)
5. Find Dictionary Length
Dictionary Length
Print the number of items in the dictionary:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
print(len(man))
6. Adding Items Dictionary
Adding an item to the dictionary is done by using a new index key and assigning a value to it:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
man[“color”] = “white”
print(man)
7. Removing Items
There are several methods to remove items from a dictionary:
Examples
a. The pop() method removes the item with the specified key name:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
man.pop(“study”)
print(man)
b. The popitem() method removes the last inserted item
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
man.popitem()
print(man)
c. The del keyword removes the item with the specified key name:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
del man[“age”]
print(man)
d. The del keyword can also delete the dictionary completely:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
del man
print(man) # Error
e. The clear() keyword empties the dictionary:
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
man.clear()
print(man)
8. Copy a Dictionary
There are ways to make a copy, one way is to use the built-in Dictionary method copy().
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
newman= man.copy()
print(newman)
Another way to make a copy is to use the built-in method dict().
man = {
“name”: “Venkat”,
“study”: “Engineering”,
“age”: 24
}
newman = dict(man)
print(newman)
9. Nested Dictionaries
10. The dict() Constructor