Dictionary in Python : Practice

Dictionaries in Python:¶

1) key and value pair
2) Key and value can be any datatype
3) Unordered pair
4) keyError
5) in and not in
6) keys(), values(), items()
7) get(key, user defined return value) -> returns a default value if key doesn't exist.
8) setdefault(key:value) -> sets a value if key doesn't exist
9) pprint.pprit() (pretty print)
10) It's mutable

key and value pair:¶

In [1]:

#dict = {key:value}
#Example:
student = {"mike":25, "alex": 35, "tom": 22,"alice":27}
print(student)

{'tom': 22, 'mike': 25, 'alice': 27, 'alex': 35}

Key and value can be any datatype¶

In [3]:

sample_dict = {"string":"string", "string":10,10:200, 1.02:5.5, 1.09:"check"}
print(sample_dict)

{'string': 10, 10: 200, 1.09: 'check', 1.02: 5.5}

Unordered pair¶

List is an ordered pair, but dictionary is an unordered pair.

In [4]:

a = [1,2,3]
b = [3,2,1]
print(a == b)
class1 = {"mike":25, "alex": 35, "tom": 22,"alice":27}
class2 = {"alice":27,"alex":35,"mike":25,"tom":22}
print(class1 == class2)

False
True

KeyError in dict¶

Always check whether the key is in dict before accessing it.

In [5]:

student = {"mike":25, "alex": 35, "tom": 22,"alice":27}
print(student["george"])

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-5-ca59a2aa0687> in <module>()
      1 student = {"mike":25, "alex": 35, "tom": 22,"alice":27}
----> 2 print(student["george"])

KeyError: 'george'

In [6]:

if "george" in student:
    print(student["george"])

in and not in¶

In [7]:

print("mike" in student)
print("mike" not in student)
print("arun" not in student)

True
False
True

keys(), values(), items()¶

In [8]:

print(student.keys()) # key list
print(student.values()) # value list
print(student.items()) # key,value tuple

dict_keys(['tom', 'mike', 'alice', 'alex'])
dict_values([22, 25, 27, 35])
dict_items([('tom', 22), ('mike', 25), ('alice', 27), ('alex', 35)])

In [9]:

for k,v in student.items():
    print(k,v)

tom 22
mike 25
alice 27
alex 35

get() :¶

It returns a default value if key doesn't exist

In [10]:

print(student.get("mike",10))
print(student.get("george",10))

25
10

setdefault()¶

In [13]:

student.setdefault("linda",29)
print(student)
student.setdefault("linda",40) # It won't update the value because linda is already in our dict
print(student)

{'tom': 22, 'mike': 25, 'linda': 29, 'alice': 27, 'alex': 35}
{'tom': 22, 'mike': 25, 'linda': 29, 'alice': 27, 'alex': 35}

In [16]:

s = "hi how are you? my name is arun prakash."
count_dict = {}
for letter in s:
    count_dict.setdefault(letter,0)
    count_dict[letter] = count_dict[letter] +1
print(count_dict)

{' ': 8, 'a': 5, 'k': 1, 'm': 2, 'p': 1, 'o': 2, '.': 1, 'u': 2, 's': 2, 'w': 1, 'i': 2, 'r': 3, '?': 1, 'n': 2, 'h': 3, 'e': 2, 'y': 2}

In [17]:

import pprint
pprint.pprint(count_dict)

{' ': 8,
 '.': 1,
 '?': 1,
 'a': 5,
 'e': 2,
 'h': 3,
 'i': 2,
 'k': 1,
 'm': 2,
 'n': 2,
 'o': 2,
 'p': 1,
 'r': 3,
 's': 2,
 'u': 2,
 'w': 1,
 'y': 2}

In [ ]: