14 Basic Python Exercises with Solutions

1. Grade Classification

Input a percentage score and output grade A‑E using if statements, with validation for unreasonable scores.

<code>a = eval(input('请输入成绩：'))
if a < 0 or a > 100 or a % 1 != 0:
    print('您输入的成绩不合理，请检查后重新输入')
elif 90 <= a <= 100:
    print('成绩等级:A')
elif 80 <= a <= 89:
    print('成绩等级:B')
elif 70 <= a <= 79:
    print('成绩等级:C')
elif 60 <= a <= 69:
    print('成绩等级:D')
else:
    print('成绩等级:E')</code>

2. Basketball Safety Algorithm

Determine whether a lead in a basketball game is "safe" based on remaining time, lead points, and ball possession.

<code>grade = eval(input('请输入领先分数:'))
time = eval(input('请输入剩余时间:'))
t = grade - 3
w = input('目前是否为领先队控球（Y or N）：')
if w == 'Y' or w == 'y':
    g = (t + 0.5) ** 2
else:
    g = (t - 0.5) ** 2
if g < 0:
    g = 0
if g > time:
    print('领先是“安全”的')
else:
    print('领先是“不安全”的')
</code>

3. Series Sum y = 1+3‑1+3‑1+…+(2n‑1)‑1

Find the maximum n such that y < 3 and the corresponding y value.

<code>x = 1
y = 0
while y < 3:
    y = y + 1/(2*x-1)
    x = x + 1
print('y<3时的最大n值为{}'.format(x-1))
print('与(1)的n值对应的y值为{}'.format(y-1/(2*x-1)))
</code>

4. Shopping Card Combination

Find all ways to spend exactly 100 元 on shampoo (15 元), soap (2 元), and toothbrushes (5 元).

<code>money = 100
n = money // 15
for i in range(n, -1, -1):
    m = (money - i*15) // 5
    for j in range(m, -1, -1):
        k = (money - i*15 - j*5) // 2
        if (money - i*15 - j*5) % 2 == 0:
            print('可选择的购买组合: 购买洗发水 {} 瓶，香皂 {} 块，牙刷 {}个。'.format(i, j, k))
</code>

5. Number Guessing Game

Generate a random integer between 1 and 100; the user has up to 7 attempts to guess it, receiving "High", "Low", or "You won!" feedback, with an option to replay.

<code>chose = 'y'
while chose == 'Y' or chose == 'y':
    import random
    num = random.randint(1, 100)
    def judge(b):
        return 1 if b == num else 0
    for i in range(1, 8):
        b = eval(input('请输入您第{}次所猜的整数：'.format(i)))
        if judge(b) == 1:
            print('You won !')
            break
        elif b > num:
            print('high')
        else:
            print('low')
    if judge(b) == 0:
        print('You lost !')
    chose = input('请输入Y(y)继续进行游戏，N(n)退出游戏：')
    while chose not in ('Y','y','N','n'):
        print('输入有误，请重新输入Y(y)继续进行游戏，N(n)退出游戏：', end='')
        chose = input()
</code>

6. Ten‑Character String with Index Access

Create a 10‑character string and output the n‑th character, defaulting to the last character for out‑of‑range indices, using try / except .

<code>n = int(input('请输入数字n：'))
a = 'pengyuanyu'
try:
    print(a[n-1])
except:
    print(a[9])
</code>

7. Function for Max, Min, and Average

Read a space‑separated list of numbers and print the maximum, minimum, and average using NumPy.

<code>import numpy as py
x = input('请输入一组数并用空格隔开：')

def f(x):
    lis = list(x.split(' '))
    for i in range(len(lis)):
        lis[i] = eval(lis[i])
    print('该组数值的最大值为：', max(lis))
    print('该组数值的最小值为：', min(lis))
    print('该组数值的平均值为：', py.mean(lis))

f(x)
</code>

8. Duck‑Counting Recursion

Calculate the initial number of ducks when after seven villages only two remain, using a recursive function.

<code>def f(n):
    if n == 8:
        return 2
    else:
        sum = f(n+1)*2 + 2
        return sum
print('一共有{}只鸭子'.format(f(1)))
</code>

9. Complex Number Parts

Assign the complex number 2.3103‑1.3410‑3j to variable A and extract its real and imaginary parts.

<code>A = complex(2.3e3, -1.34e-3)
print(A.real)
print(A.imag)
</code>

10. Expression Evaluation

Compute the value of a trigonometric expression involving math.sin and math.e .

<code>import math
z1 = (2 * (math.sin(math.pi * 85 / 180))) / (1 + math.e**2)
print(z1)
</code>

11. String Operations

Given a 10‑character string, output its length, a sub‑string taking every second character, the reversed string, and a new string combining parts of the original and reversed strings.

<code>A = input()
print(len(A))
B = A[::3]
print(B)
C = A[::-1]
print(C)
D = A[:3] + C[-5:]
print(D)
</code>

12. Number Formatting

Format the number 0.002178 as scientific notation, a float with four decimal places, and a percentage, all centered in a width of 10 with * padding.

<code>x = 0.002178
print('x对应的科学表示法形式为:'.center(10, '*'), ('%e' % x).center(10, '*'))
print('x具有4位小数精度的浮点数形式为：'.center(10, '*'), ('{0:.4f}'.format(x)).center(10, '*'))
print('x百分数形式为:'.center(10, '*'), ('{0:.2f}%'.format(x*100)).center(10, '*'))
</code>

13. Weekday Lookup

Input a number 1‑7 and output the corresponding weekday name.

<code>n = int(input('输入一个1~7的数字:'))
if n == 1:
    print('您输入的是星期一')
elif n == 2:
    print('您输入的是星期二')
elif n == 3:
    print('您输入的是星期三')
elif n == 4:
    print('您输入的是星期四')
elif n == 5:
    print('您输入的是星期五')
elif n == 6:
    print('您输入的是星期六')
elif n == 7:
    print('您输入的是星期日')
</code>

14. Four‑Digit Number Encryption

Multiply each digit of a four‑digit integer by 7, keep only the unit digit, and form a new encrypted number.

<code>n = int(input('任意输入1个4位数:'))
if 1000 <= n <= 9999:
    a = n % 10
    b = (n // 10) % 10
    c = (n // 100) % 10
    d = (n // 1000) % 10
    a = a * 7 % 10
    b = b * 7 % 10
    c = c * 7 % 10
    d = d * 7 % 10
    n = 1000*d + 100*c + 10*b + a
    print(n)
else:
    print('您输入的数字不符合要求，请输入一个四位数字')
</code>

This collection of exercises covers fundamental Python concepts such as conditional statements, loops, functions, recursion, string manipulation, numeric formatting, and basic I/O, providing ready‑to‑run code and example outputs for each problem.