Welcome / 欢迎

Interactive review for Python Class 2. Select a topic from the left to begin.

欢迎使用 Python 第2课交互式复习应用。请从左侧选择一个主题开始。

Instructions

Navigate using the sidebar.
Read the bilingual explanations.
Click Run to execute code simulations.

1. Variables & Indexing

In Python, strings are sequences. We access characters using 0-based indexing.

在 Python 中，字符串是序列。我们使用基于0的索引访问字符。

                            text = "today is our 2 lesson"

                            print(text[0])

                            print(text[13])

Iteration:

                             for i in range(len(text)):

                               print(text[i])

2. List Operations

Operators + and * behave differently on lists than numbers.

+ 和 * 运算符在列表上的行为与数字不同。

                            l1 = [2, 3]; l2 = [1, 2]

                            print(l2 + l1) # Join

                            print(l2 * 10) # Repeat

3. Loops & Modification

To modify a list in place, loop using range(len(list)).

要就地修改列表，请使用 range(len(list)) 进行循环。

                    nums = [1, 2, 3, 4]

                    # Divide every number by 10

                    for i in range(len(nums)):

                      nums[i] = nums[i] / 10

                    print(nums)

4. Algorithms (Min/Max)

Finding the smallest number: Manual Algorithm vs. Built-in Functions.

寻找最小数：手动算法 vs 内置函数。

Manual Logic

                            guess = list[0]

                            for x in list:

                              if guess > x: guess = x

Built-in (Recommended)

                            print(max(list))

                            print(min(list))

5. String Parsing

Extracting numerical data from text.

从文本中提取数值数据。

                    text = "4 students, 2 postdocs"

                    sum = 0

                    for w in text.split():

                      if w.isdigit():

                        sum += int(w)

6. Common Errors

TypeError

Caused by naming a variable max (shadowing).

NameError

Caused by using a list before creating it [].

7. Mutability Trap

Lists are mutable. b = a links them together.

列表是可变的。b = a 将它们链接在一起。

Integer (Safe)

a=1; b=a; a=2; print(b)

List (Trap!)

a=[1]; b=a; a[0]=2; print(b)

8. File I/O

Reading and writing files. Modes: "w" (write), "a" (append), "r" (read).

读写文件。模式："w"（写入），"a"（追加），"r"（读取）。

Virtual File Content

9. Visualization

Interactive equivalent of matplotlib.pyplot.

matplotlib.pyplot 的交互式等效项。

                    import matplotlib.pyplot as plt

                    x = [1, 2, 3, 4]

                    y = [1, 2, 3, 4]

                    plt.plot(x, y)