You must know about Python Dict and Set practical skills sharing

1. Dict: Magic of key-value pairs

1. Basic usage (create and access)

person = {"name": "Alice", "age": 25, "city": "Shanghai"}
print(person["name"])  #Output: Alice

2. Efficient search of dictionaries

The search speed of the dictionary is extremely fast, with a time complexity of O(1). Compared with O(n) of list, the advantages are obvious when processing large amounts of data.

3. Dictionary derivation

squares = {x: x*x for x in range(1, 6)}
print(squares)  # Output: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

4. get() method, elegantly handle KeyError

person = {"name": "Alice", "age": 25}
score = ("score", 0)
print(score)  # Output: 0

5. Correct posture for merging dictionary

a = {"x": 1, "y": 2}
b = {"y": 3, "z": 4}
c = {**a, **b}
print(c)  # Output: {'x': 1, 'y': 3, 'z': 4}

6. Things to note

dict (dictionary) does not allow a key to be created twice, but when creating a dict (dictionary), if a key value is assigned twice, the value assigned last time will be based on the value assigned to it.
dict (Dictionary) keys must be immutable, but keys can be used as numbers, strings or tuples, but lists cannot be used

Functions and methods of (Dictionary)

Methods and functions	describe
len(dict)	Calculate the number of dictionary elements
str(dict)	Output dictionary printable string representation
type(variable)	Returns the input variable type, if the variable is a dictionary, it returns the dictionary type
()	Delete all elements in the dictionary
()	Return a shallow copy of a dictionary
()	Return all values in the dictionary as a list
popitem()	Randomly return and delete a pair of keys and values in the dictionary
()	Returns a traversable array of (keys, values) tuples as a list

2. Set (set): a tool for deduplication and efficient calculation

1. Basic usage (create)

set1=set([123,456,789])
print(set1)
fruits = {"apple", "banana", "orange"}
("pear")
print(fruits)

2. Set to remove heavy weight

nums = [1, 2, 2, 3, 4, 4, 5]
unique_nums = set(nums)
print(unique_nums)  # Output: {1, 2, 3, 4, 5}

3. Efficient operation of collections

Intersection:&
Union:|
Differences:-

a = {1, 2, 3}
b = {2, 3, 4}
print(a &amp; b)  # Output: {2, 3}print(a | b)  # Output: {1, 2, 3, 4}print(a - b)  # Output: {1}

4. Set derivation

even = {x for x in range(10) if x % 2 == 0}
print(even)  # Output: {0, 2, 4, 6, 8}

3. Summary

DictSuitable for storage mapping relationships, extremely fast search speed

SetSuitable for deduplication and set operations, high efficiency

Master derivation, merging, deduplication and other techniques to make your code more Pythonic!

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