实验4

试验任务1：

print(sum)
sum = 42
print(sum)
def inc(n):
  sum = n+1
  print(sum)
  return sum
sum = inc(7) + inc(7)
print(sum)

这4处使用的标识符sum是代表一个变量名吗？如果不是，请分别指出这4行中变量sum的作用域。

不是。1.内置作用域2.全局作用域3.局部作用域4.全局作用域

实验任务2：

list1=[1,9,8,4]
print(sorted(list1))
print(sorted(list1, reverse=True))
print(sorted(list1, True))

python内置函数sorted()中，参数reverse的传递方式是否必须使用关键字传递？

需要。

def func(a, b, c, /, *, d, e, f):
  return([a,b,c,d,e,f])
print(func(1,2,3,d=4,e=5,f=6))

实验任务3：

def solve(a, b, c):
  '''
  求解一元二次方程, 返回方程的两个根
  :para: a,b,c: int 方程系数
  :return: tuple
  '''
  delta = b*b - 4*a*c
  delta_sqrt = abs(delta)**0.5
  p1 = -b/2/a;
  p2 = delta_sqrt/2/a
  if delta>=0:
    root1 = p1 + p2
    root2 = p1 - p2
  else:
    root1 = complex(p1, p2)
    root2 = complex(p1, -p2)
  return root1, root2
print(solve.__doc__)
while True:
  try:
    a,b,c = eval(input('Enter eqution coefficient: '))
    if a == 0:
      raise
  except:
    print('invalid input, or, a is zero')
    break
  else:
    root1, root2 = solve(a, b, c)
    print(f'root1 = {root1:.2f}, root2 = {root2:.2f}')
    print()

实验任务4：

def list_generator(a,b,step=1):
    list=[]
    i=a
    while a<=i<=b:
        list.append(i)
        i+=step
    return list
list1 = list_generator(-5, 5)
print(list1)
list2 = list_generator(-5, 5, 2)
print(list2)
list3 = list_generator(1, 5, 0.5)
print(list3)

实验任务5：

def is_prime(num):
    if num>1:
        for i in range(2,num//2+1):
            if num%i==0:
                return False
                break
        else:
            return True
    else:
        return False
for a in range(0,21):
    if a%2==0:
        for i in range(2,a):
            if is_prime(a-i):
                print(f'{a}={i}+{a-i}')
                break

实验任务6：

def encoder(n):
    list=[]
    for i in n:
        i = ord(i)
        if 97 <= i <= 117 or 65 <= i <= 85:
            i = i + 5
        elif 117 < i <= 122 or 85 < i <= 90:
            i = i - 21
        else:
            i = i
        list.append(chr(i))
    return ''.join(list)
def decoder(n):
    n=encoder(n)
    list=[]
    for i in n:
        i=ord(i)
        if 102 <= i <= 122 or 70 <= i <= 90:
            i=i-5
        elif 97 <= i < 102 or 65 <= i < 70:
            i=i+21
        else:
            i=i
        list.append(chr(i))
    return ''.join(list)
n = input('输入英文文本：')
print('编码后' + encoder(n))
print('编码后' + decoder(n))

实验任务7：

def collatz(n):
    if n%2==0:
        return n/2
    else:
        return 3*n+1
try:
    a=eval(input('Enter a positive integer:'))
    if int(a)!=a or a<=0:
        raise ValueError and NameError
except ValueError and NameError:
    print('Error: must be a positive integer')
else:
    list=[a]
    while a!=1:
        a=collatz(a)
        list.append(a)
    print(list)