Python learning tips: use the default behavior of dictionaries, and python tips

Python learning tips: use the default behavior of dictionaries, and python tips

This article describes Python's usage of the dictionary's default behavior and shares it with you for your reference. Let's take a look at the details below:

Typical code 1:

from collections import defaultdict   if __name__ == '__main__':  data = defaultdict(int)  data[0] += 1  print(data) 

Output 1:

defaultdict(<type 'int'>, {0: 1}) 

Typical Code 2:

if __name__ == '__main__':  data = {'k': 1}  data.setdefault('k', 100)  data.setdefault('k1', -100)  print(data) 

Output 2:

{'k': 1, 'k1': -100} 

Application scenarios:

Application scenarios of typical code 1:

When writing some statistical code, you always need to count the number of keys and use a dictionary to store the counting results. If you use a classic dictionary, every time, we need to manually write code to determine whether the corresponding key exists. If it does not exist, we need to store it in this dictionary and initialize it to 0. Instead, we use the defaultdict data type, we can directly specify a factory function to generate default values for us. Typical code 1 uses the built-in int function, and of course it can also be an anonymous function defined by lambda expressions.

Application scenarios of typical code 2:

For a dictionary, if we only want to keep the value specified for each key for the first time, if we use the traditional method data ['K'] = 'V, we need to determine whether the corresponding key exists in the dictionary every time before deciding whether to set the value of this key. 2. Using the setdefault method of dict, we can avoid this judgment, implement this function in a more concise way.

Benefits:

1. The setdefault method in scenario 2 is optimized in the implementation of the Python interpreter. Generally, it is more efficient to execute Python code with the same functions as the one you write.

2. Both of these default scenarios make the code more compact, logically, and more efficient to read the code.

Other Instructions:

1. The defaultdict type can receive many types. The built-in list, set, and dict functions can be used directly. lambda anonymous functions can be used to define their own types.

Summary

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