1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344<div align="center">
<h1> 30 Days Of Python: Day 8 - Dictionaries</h1>
<a class="header-badge" target="_blank" href="https://www.linkedin.com/in/asabeneh/">
<img src="https://img.shields.io/badge/style--5eba00.svg?label=LinkedIn&logo=linkedin&style=social">
</a>
<a class="header-badge" target="_blank" href="https://twitter.com/Asabeneh">
<img alt="Twitter Follow" src="https://img.shields.io/twitter/follow/asabeneh?style=social">
</a>
<sub>Author:
<a href="https://www.linkedin.com/in/asabeneh/" target="_blank">Asabeneh Yetayeh</a><br>
<small>June 2021</small>
</sub>
</div>
</div>
[<< Day 7 ](../07_Day_Sets/07_sets.md) | [Day 9 >>](../09_Day_Conditionals/09_conditionals.md)
<!--  -->
- [📘 Day 8](#-day-8)
- [Dictionaries](#dictionaries)
- [Creating a Dictionary](#creating-a-dictionary)
- [Dictionary Length](#dictionary-length)
- [Accessing Dictionary Items](#accessing-dictionary-items)
- [Adding Items to a Dictionary](#adding-items-to-a-dictionary)
- [Modifying Items in a Dictionary](#modifying-items-in-a-dictionary)
- [Checking Keys in a Dictionary](#checking-keys-in-a-dictionary)
- [Removing Key and Value Pairs from a Dictionary](#removing-key-and-value-pairs-from-a-dictionary)
- [Changing Dictionary to a List of Items](#changing-dictionary-to-a-list-of-items)
- [Clearing a Dictionary](#clearing-a-dictionary)
- [Deleting a Dictionary](#deleting-a-dictionary)
- [Copy a Dictionary](#copy-a-dictionary)
- [Getting Dictionary Keys as a List](#getting-dictionary-keys-as-a-list)
- [Getting Dictionary Values as a List](#getting-dictionary-values-as-a-list)
- [💻 Exercises: Day 8](#-exercises-day-8)
# 📘 Day 8
## Dictionaries
A dictionary is a collection of unordered, modifiable(mutable) paired (key: value) data type.
### Creating a Dictionary
To create a dictionary we use curly brackets, {}.
```py
# syntax
empty_dict = {}
# Dictionary with data values
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
```
**Example:**
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python']
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
```
The dictionary above shows that a value could be any different data type:string, boolean, list, tuple, set or a dictionary.
### Dictionary Length
It checks the number of 'key: value' pairs in the dictionary.
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
print(len(dct)) # 4
```
**Example:**
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
print(len(person)) # 7
```
### Accessing Dictionary Items
We can access Dictionary items by referring to its key name.
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
print(dct['key1']) # value1
print(dct['key4']) # value4
```
**Example:**
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
print(person['first_name']) # Asabeneh
print(person['country']) # Finland
print(person['skills']) # ['JavaScript', 'React', 'Node', 'MongoDB', 'Python']
print(person['skills'][0]) # JavaScript
print(person['address']['street']) # Space street
print(person['city']) # Error
```
Accessing an item by key name raises an error if the key does not exist. To avoid this error first we have to check if a key exist or we can use the _get_ method. The get method returns None, which is a NoneType object data type, if the key does not exist.
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
print(person.get('first_name')) # Asabeneh
print(person.get('country')) # Finland
print(person.get('skills')) #['HTML','CSS','JavaScript', 'React', 'Node', 'MongoDB', 'Python']
print(person.get('city')) # None
```
### Adding Items to a Dictionary
We can add new key and value pairs to a dictionary
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
dct['key5'] = 'value5'
```
**Example:**
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
person['job_title'] = 'Instructor'
person['skills'].append('HTML')
print(person)
```
### Modifying Items in a Dictionary
We can modify items in a dictionary
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
dct['key1'] = 'value-one'
```
**Example:**
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
person['first_name'] = 'Eyob'
person['age']
```
### Checking Keys in a Dictionary
We use the _in_ operator to check if a key exist in a dictionary
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
print('key2' in dct) # True
print('key5' in dct) # False
```
### Removing Key and Value Pairs from a Dictionary
- _pop(key)_: removes the item with the specified key name:
- _popitem()_: removes the last item
- _del_: removes an item with specified key name
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
dct.pop('key1') # removes key1 item
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
dct.popitem() # removes the last item
del dct['key2'] # removes key2 item
```
**Example:**
```py
person = {
'first_name':'Asabeneh',
'last_name':'Yetayeh',
'age':250,
'country':'Finland',
'is_marred':True,
'skills':['JavaScript', 'React', 'Node', 'MongoDB', 'Python'],
'address':{
'street':'Space street',
'zipcode':'02210'
}
}
person.pop('first_name') # Removes the firstname item
person.popitem() # Removes the address item
del person['is_married'] # Removes the is_married item
```
### Changing Dictionary to a List of Items
The _items()_ method changes dictionary to a list of tuples.
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
print(dct.items()) # dict_items([('key1', 'value1'), ('key2', 'value2'), ('key3', 'value3'), ('key4', 'value4')])
```
### Clearing a Dictionary
If we don't want the items in a dictionary we can clear them using _clear()_ method
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
print(dct.clear()) # None
```
### Deleting a Dictionary
If we do not use the dictionary we can delete it completely
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
del dct
```
### Copy a Dictionary
We can copy a dictionary using a _copy()_ method. Using copy we can avoid mutation of the original dictionary.
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
dct_copy = dct.copy() # {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
```
### Getting Dictionary Keys as a List
The _keys()_ method gives us all the keys of a a dictionary as a list.
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
keys = dct.keys()
print(keys) # dict_keys(['key1', 'key2', 'key3', 'key4'])
```
### Getting Dictionary Values as a List
The _values_ method gives us all the values of a a dictionary as a list.
```py
# syntax
dct = {'key1':'value1', 'key2':'value2', 'key3':'value3', 'key4':'value4'}
values = dct.values()
print(values) # dict_values(['value1', 'value2', 'value3', 'value4'])
```
🌕 You are astonishing. Now, you are super charged with the power of dictionaries. You have just completed day 8 challenges and you are 8 steps a head in to your way to greatness. Now do some exercises for your brain and for your muscle.
## 💻 Exercises: Day 8
1. Create an empty dictionary called dog
2. Add name, color, breed, legs, age to the dog dictionary
3. Create a student dictionary and add first_name, last_name, gender, age, marital status, skills, country, city and address as keys for the dictionary
4. Get the length of the student dictionary
5. Get the value of skills and check the data type, it should be a list
6. Modify the skills values by adding one or two skills
7. Get the dictionary keys as a list
8. Get the dictionary values as a list
9. Change the dictionary to a list of tuples using _items()_ method
10. Delete one of the items in the dictionary
11. Delete one of the dictionaries
🎉 CONGRATULATIONS ! 🎉
[<< Day 7 ](../07_Day_Sets/07_sets.md) | [Day 9 >>](../09_Day_Conditionals/09_conditionals.md)