Python dictionary derivation can be used to concisely create or convert dictionaries. 1. You can generate key-value pairs from a list, such as {word: len(word) for word in words}; 2. Support conditional filtering, such as adding if len(word) > 4; 3. You can build dictionaries from two lists with zip; 4. You can convert the values of existing dictionaries, such as v.upper(); 5. You can reverse key-value pairs, provided that the value is a hashable type; dictionary derivation is efficient and readable, but excessive nesting should be avoided. It is recommended to implement complex logic by loops.
Python dictionary derivation is a concise way to quickly create dictionaries based on an iterable object. Its syntax is similar to list comprehension, but uses curly braces {} and specifies key-value pairs.
Basic syntax:
{key: value for item in iterable}1. Basic example: Create a dictionary from a list
Suppose you want to convert a list of strings into a dictionary, the key is a string, and the value is the length of the string:
words = ['apple', 'banana', 'cat']
word_length = {word: len(word) for word in words}
print(word_length)
# Output: {'apple': 5, 'banana': 6, 'cat': 3}2. Dictionary derivation with conditional filtering
Only words with length greater than 4 are retained:
words = ['apple', 'hi', 'banana', 'cat']
long_words = {word: len(word) for word in words if len(word) > 4}
print(long_words)
# Output: {'apple': 5, 'banana': 6}3. Create a dictionary from two lists (using zip)
keys = ['name', 'age', 'city']
values = ['Alice', 25, 'New York']
person = {k: v for k, v in zip(keys, values)}
print(person)
# Output: {'name': 'Alice', 'age': 25, 'city': 'New York'}4. Convert existing dictionary (for example: convert all values to uppercase)
original = {'a': 'hello', 'b': 'world'}
uppercase = {k: v.upper() for k, v in original.items()}
print(uppercase)
# Output: {'a': 'HELLO', 'b': 'WORLD'}5. Invert the keys and values of the dictionary
original = {'one': 1, 'two': 2, 'three': 3}
reversed_dict = {v: k for k, v in original.items()}
print(reversed_dict)
# Output: {1: 'one', 2: 'two', 3: 'three'}?? Note: It can only be reversed if the value of the original dictionary is a hashable type (such as strings, numbers).
Tips:
- Dictionary derivation is very efficient and suitable for processing data transformation.
- Good readability, but don't nest it too deeply.
- If the logic is complicated, it is recommended to use a normal loop instead.
Basically these common uses are not complicated but very practical.
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