python dictionary example
Python dictionary is used to store key-value pairs, which can be created through curly braces or dict(). 1. Create: initialize with {} or dict(); 2. Access: Get the value through the key or get() method, the latter can set the default value; 3. Modify and add: directly assign values to modify or add key-value pairs; 4. Delete: Use del or pop() to remove key-value pairs, and pop() can return deleted values; 5. Traversal: Use for loops to combine keys(), values() or items() methods; 6. Application: For example, counting word frequency is calculated, counting is achieved through loops and get(). Dictionary is widely used in JSON processing, cache and configuration management scenarios. Mastering its addition, deletion, modification, and traversal operations can meet most actual needs.
The Python dictionary is a very common data structure used to store key-value pairs. Here are a few common examples to help you quickly understand and use Python dictionaries.
1. Basic ways to create dictionaries
# Method 1: Use curly braces {}
student = {
"name": "Alice",
"age": 20,
"major": "Computer Science",
"is_enrolled": True
}
# Method 2: Use dict() constructor person = dict(name="Bob", age=25, city="Beijing")
print(student)
# Output: {'name': 'Alice', 'age': 20, 'major': 'Computer Science', 'is_enrolled': True}2. Access the value in the dictionary
You can get the corresponding value through the key:
print(student["name"]) # Output: Alice
print(student.get("age")) # Output: 20
# Use get() to avoid errors when the key does not exist print(student.get("grade", "Not Found")) # Output: Not Found (returns the default value when the key does not exist)3. Modify and add key-value pairs
# Modify the value of the existing key student["age"] = 21 # Add new key value pair student["university"] = "Tsinghua University" print(student) # Output: Dictionary containing updated age and new university
4. Delete key-value pairs
# Delete the specified key del student["is_enrolled"]
# Or use the pop() method (can also get deleted values)
major = student.pop("major")
print(major) # Output: Computer Science
print(student)
# Output: {'name': 'Alice', 'age': 21, 'university': 'Tsinghua University'}5. Traversing the dictionary
for key in student:
print(key, ":", student[key])
# A clearer way:
for key, value in student.items():
print(f"{key}: {value}")Output:
name: Alice age: 21 university: Tsinghua University
6. Common application scenario examples: statistical word frequency
text = "apple banana apple orange banana apple"
word_count = {}
for word in text.split():
word_count[word] = word_count.get(word, 0) 1
print(word_count)
# Output: {'apple': 3, 'banana': 2, 'orange': 1}Basically that's it. Dictionaries are used very frequently in actual development, such as processing JSON data, caching, configuration management, etc. By mastering the operations of adding, deleting, revising and traversing, you can deal with most scenarios.
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