Python Lists & Dictionaries: Master Key Data Structures in 5 Minutes

1. List (list): batch data container

Core idea: a list can store any type of data (numbers, strings), is mutable, iterable, and is the most frequently used data structure.

# 1. Define a list (using [] and commas)
scores = [88, 95, 70, 66, 92]  # store grades
names = ["张三", "李四", "王五"]  # store names
mix = [18, "Python", 62.5, True]  # mixed types are allowed

# 2. Core operations (use directly, must master)
print(scores[0])               # get first element, outputs: 88
scores.append(85)               # add element, result: [88, 95, 70, 66, 92, 85]
scores.remove(70)               # delete specific element, result: [88, 95, 66, 92, 85]
scores[2] = 75                 # modify element, result: [88, 95, 75, 92, 85]
print(len(scores))              # view length, outputs: 5

# 3. Combine with for‑loop for high‑frequency practice
for name in names:
    print("姓名：", name)
for s in scores:
    if s >= 80:
        print(s, "合格")

2. Dictionary (dict): key‑value storage for precise lookup

Core idea: each key maps to a value, forming a one‑to‑one correspondence, similar to a phone book (name → phone).

# 1. Define a dictionary (using {} and colon)
student = {
    "name": "张三",
    "age": 18,
    "score": 88,
    "is_student": True
}

# 2. Core operations (use directly, must master)
print(student["name"])          # fetch by key, outputs: 张三
student["score"] = 90            # modify value, score becomes 90
student["gender"] = "男"       # add new key‑value pair
del student["is_student"]       # delete a key‑value pair

# 3. Iterate over a dictionary (two common ways)
# Way 1: iterate over all keys
for key in student:
    print(key, ":", student[key])
# Way 2: iterate over key‑value pairs (more concise)
for key, value in student.items():
    print(key, ":", value)

3. Combined practice: list of dictionaries

# Store multiple students (list of dicts)
students = [
    {"name": "张三", "age": 18, "score": 88},
    {"name": "李四", "age": 19, "score": 95},
    {"name": "王五", "age": 17, "score": 76}
]

# Iterate and print "name + score", check pass/fail
for stu in students:
    name = stu["name"]
    score = stu["score"]
    if score >= 60:
        print(f"{name}，成绩：{score}，及格")
    else:
        print(f"{name}，成绩：{score}，不及格")

4. Four common pitfalls for beginners (with solutions)

❌ Pitfall 1: List index out of range (e.g., scores[10] when list has 5 elements). Solution: Index must be within 0‑(len(list)‑1); use len(list) to check length first.

❌ Pitfall 2: Dictionary key error (e.g., student["phone"] when key does not exist). Solution: Use dict.get("phone", "无此键") for safe lookup.

❌ Pitfall 3: Incorrect modification syntax (assigning to a list with =, or using unquoted Chinese keys in a dict). Solution: Modify lists with append / remove /index assignment; dict keys must be quoted strings.

❌ Pitfall 4: Installing packages via Alibaba or Douban mirrors fails with "webpage parsing error". Solution: Switch to alternative mirrors, preferably Tsinghua's (

pip install -i https://pypi.tuna.tsinghua.edu.cn/simple 包名

) or USTC's as backup.

5. Post‑lesson mini‑tasks (5‑minute copy‑and‑run)

# 1. List: define 5 numbers, add one, remove one, print final list
nums = [10, 20, 30, 40, 50]
nums.append(60)
nums.remove(30)
print(nums)

# 2. Dictionary: store personal info, modify weight, print all pairs
my_info = {"name": "Your Name", "age": 25, "weight": 70}
my_info["weight"] = 68
for k, v in my_info.items():
    print(k, ":", v)

# 3. List of dictionaries: store two classmates, print name and score
classmates = [
    {"name": "同学1", "score": 85},
    {"name": "同学2", "score": 92}
]
for classmate in classmates:
    print(classmate["name"], "成绩：", classmate["score"])

6. Key takeaways

Lists enable batch data storage; dictionaries provide precise key‑value mapping—both are foundations for later practical scenarios such as office automation and web crawling.

Essential skills to master today: list append / remove /index assignment, dictionary get/modify/iterate, and nesting lists within dictionaries.

When errors occur, first check list indices, dictionary keys, and package‑install mirrors (prefer Tsinghua or USTC mirrors over Alibaba/Douban).