#14 - Python Dictionary

#14 - Python Dictionary

By Ifeanyi Omeata

Ifeanyi Omeata's photo
Ifeanyi Omeata
·

6 min read

Topics:

1. Python Collections
2. Dictionaries
3. Dictionary Length
4. Dictionary Items Data Types
5. Accessing Dictionary Items
6. Get Dictionary Keys
7. Get Dictionary Values
8. Get Dictionary Items
9. Check if Dictionary Key Exists
10. Change Dictionary Values
11. Update Dictionary Values
12. Add Dictionary Items
13. Remove Dictionary Items
14. Loop through Dictionary
15. Copy a Dictionary
16. Nested Dictionaries
17. Dictionary fromkeys() Method
18. Dictionary setdefault() Method
19. Dictionary List pairing
20. Dictionary List pairing with Zip
21. Dictionary List pairing with Zip_longest

1. Python Collections

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There are four collection data types in the Python programming language:

  • List is a collection which is ordered and changeable. Allows duplicate members.
  • Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
  • Set is a collection which is unordered, unchangeable, and unindexed. No duplicate members.
  • Dictionary is a collection which is ordered and changeable. No duplicate members.

2. Dictionaries

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A dictionary is a collection which is ordered, changeable and do not allow duplicates.

  • Dictionaries are ordered, meaning that the items have a defined order, and that order will not change.
  • Dictionaries are changeable, meaning that we can change, add or remove items after the dictionary has been created.
  • Dictionaries cannot have two items with the same key.

Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

student =    {
  "name": "Paul",
  "age": 32,
  "year of graduation": 2020
}
print(student)

image.png

student =    {
  "name": "Paul",
  "age": 32,
  "year of graduation": 2020
}
print(student['name'])

image.png

3. Dictionary Length

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Use the len() function to determine how many items a dictionary has.

student =    {
  "name": "Paul",
  "age": 32,
  "year of graduation": 2020
}

print(len(student))

image.png

4. Dictionary Items Data Types

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

print(type(mydict['brand']))
print(type(mydict['electric']))
print(type(mydict['year']))
print(type(mydict['colors']))
print(type(mydict))

image.png

5. Accessing Dictionary Items

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

print(mydict.get('year'))
print(mydict['colors'])

image.png

6. Get Dictionary Keys

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The keys() method will return a list of all the keys in the dictionary.

mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

print(mydict.keys())

for index,key in enumerate(mydict.keys()):
  print(index,key)

image.png

7. Get Dictionary Values

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

print(mydict.values())

for index,value in enumerate(mydict.values()):
  print(index,value)

image.png

8. Get Dictionary Items

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

print(mydict.items())

for index,item in enumerate(mydict.items()):
  print(index,item)

image.png

9. Check if Dictionary Key Exists

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

if 'year' in mydict:
  print(f"The value of key (year) is {mydict.get('year')}.")
else:
  print('year is not a key in mydict.')

image.png

10. Change Dictionary Values

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

mydict['year'] = 2001

for item in mydict.items():
  print(item)

image.png

11. Update Dictionary Values

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

mydict.update({'brand':'Tesla','colors':["black","white"]})

for item in mydict.items():
  print(item)

image.png

12. Add Dictionary Items

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Adding an item to the dictionary is done by using a new index key and assigning a value to it.

mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

mydict['is_new'] = True
mydict.update({'rating':8})

for item in mydict.items():
  print(item)

image.png

13. Remove Dictionary Items

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  • The pop() method removes the item with the specified key name.
  • The popitem() method removes the last inserted item.
  • The del keyword removes the item with the specified key name.
  • The clear() method empties the dictionary.
mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"],
  "is_new": True,
  "rating": 8
}

print('#popitem() --> "rating"')
mydict.popitem()

print('#pop() --> "colors"')
mydict.pop('colors')

print('#del --> "is_new"')
del mydict['is_new']

print('#clear() --> empty_dict')
mydict.clear()

image.png

14. Loop through Dictionary

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When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"],
  "is_new": True,
  "rating": 8
}
for x in mydict:
  print(x)

image.png

mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"],
  "is_new": True,
  "rating": 8
}
for x in mydict:
  print(mydict[x])

image.png Loop through both keys and values, by using the items() method:

mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"],
  "is_new": True,
  "rating": 8
}

for key, value in mydict.items():
  print(key, value)

image.png

15. Copy a Dictionary

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mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"],
  "is_new": True,
  "rating": 8
}

thisdict = mydict.copy()
print(thisdict)

image.png

mydict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"],
  "is_new": True,
  "rating": 8
}

thisdict = dict(mydict)
print(thisdict)

image.png

16. Nested Dictionaries

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classA = {
  "student1" : {
    "name" : "Schum",
    "age" : 20
  },
  "student2" : {
    "name" : "Toby",
    "age" : 17
  },
  "student3" : {
    "name" : "Jake",
    "age" : 23
  }
}

print(classA)

image.png

17. Dictionary fromkeys() Method

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x = ('key1', 'key2', 'key3')
y = 10

mydict = dict.fromkeys(x, y)
print(mydict)

image.png

x = ('key1', 'key2', 'key3')

mydict = dict.fromkeys(x)

print(mydict)

image.png

18. Dictionary setdefault() Method

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The setdefault() method returns the value of the item with the specified key. If the key does not exist, insert the key, with the specified value.
Get the value of the "color" item, if the "color" item does not exist, insert "color" with the value "white":

car = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

x = car.setdefault("color", "white")

print(x)
print(car)

image.png

19. Dictionary List pairing

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students = ["James","Bond","Mary","Samson","Prof"]
scores = [48,72,91]

dict_student = {students[i]:scores[i] for i in range(len(scores))}
print(dict_student)

image.png

20. Dictionary List pairing with Zip

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students = ["James","Bond","Mary","Samson","Prof"]
scores = [48,72,91]

dict_student = zip(students,scores)
print(dict_student)

dict_student = list(zip(students,scores))
print(dict_student)

dict_student = {i:j for i,j in list(zip(students,scores))}
print(dict_student)

dict_student = dict(zip(students,scores))
print(dict_student)

image.png

21. Dictionary List pairing with Zip_longest

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import itertools

students = ["James","Bond","Mary","Samson","Prof"]
scores = [48,72,91]

dict_student = itertools.zip_longest(students,scores)
print(dict_student)

dict_student = dict(itertools.zip_longest(students,scores))
print(dict_student)

image.png

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