In-Depth Analysis of Python Dictionaries

In Python, a dictionary consists of a series of key-value pairs, where each key has a corresponding value. Unlike lists, the elements of a dictionary do not have a fixed order and can be quickly accessed by their keys.

1. Basic Operations on Dictionaries

Creating a dictionary is very simple:

# Create an empty dictionaryempty_dict = {}# Dictionary with initial key-value pairsuser = {    'name': 'Alice',    'age': 30,    'city': 'New York'}

For an existing dictionary, we can perform the following basic operations:

1. Viewing:

user['name']# This can also be done asuser.get('name')

Output:

'Alice'

2. Adding key-value pairs:

user['edu'] = 'Peking University'# This can also be done asuser.update({'edu':'Peking University','Nation':'China'})

3. Modifying values (keys cannot be modified):

user['age'] = 31# This can also be done asuser.update({'age':31})

Careful readers may have noticed that update can add multiple elements and also update existing elements’ values.4. Deleting key-value pairs:

del user['edu']# This can also be done asuser.pop('Nation')

2. Iterating Over Dictionaries

During data analysis, we often need to process all keys or values in a dictionary:1. Iterating over key-value pairs:

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

Output:

name Aliceage 30city New York

The above shows how to process key-value pairs together; sometimes we need to process keys and values separately, as follows:2. Iterating over keys:

for k in user.keys():    print(k)

Output:

nameagecity

3. Iterating over values:

for v in user.values():    print(v)

Output:

Alice30New York

3. Dictionary Error Handling

Accessing a non-existent key in a dictionary will raise an error.

user['office']

Output:

Traceback (most recent call last):  File "<stdin>", line 1, in <module>KeyError: 'office'

Solution: Add the target as a new key-value pair.

user.setdefault('office','1025')

Output:

'1025'

At this point, the dictionary now has an ‘office’ key. In fact, the setdefault method is similar to the get method, both are used to retrieve a key’s value. The difference is that get does not raise an error for non-existent keys and does not return any value (which is not beneficial for program development analysis). The setdefault method, however, will add the target key as a new key if it does not exist.

{'name': 'Alice', 'age': 30, 'city': 'New York', 'office': '1025'}

4. Merging Dictionaries

If there are multiple dictionaries to merge, you can use the “|” symbol.

dict0={1:'a',2:'b'}dict1={1:'c',3:'d'}print(dict0|dict1)

Output:

{1: 'c', 2: 'b', 3: 'd'}

Note that using the “|” symbol to merge does not change the original dictionaries but generates a new dictionary.

5. Conclusion

Dictionaries are one of the most commonly used data structures in Python. In data analysis work, we often need to store key-value data, such as the relationship between user IDs and names, product pricing information, etc. In summary, dictionaries provide a quick solution and are frequently used by those who work with pandas.

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