Python 怎么定义计算N的阶乘的函数

def frac(n):
  r = 1
  if n<=1:
    if n==0 or n==1:
      return 1
    else:
      print('n 不能小于0')
  else:
    for i in range(1, n+1):
      r *= i
    return r
print(frac(5))   
print(frac(6))
print(frac(7))

def frac(n):
  if n<=1:
    if n==0 or n==1:
      return 1
    else:
      print('n 不能小于0')
  else:
    return n * frac(n-1)
  
print(frac(5))
print(frac(6))
print(frac(7))

import functools
print(help(functools.reduce))

Help on built-in function reduce in module _functools:
reduce(...)
  reduce(function, sequence[, initial]) -> value
  
  Apply a function of two arguments cumulatively to the items of a sequence,
  from left to right, so as to reduce the sequence to a single value.
  For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
  ((((1+2)+3)+4)+5). If initial is present, it is placed before the items
  of the sequence in the calculation, and serves as a default when the
  sequence is empty.

import functools
def fn(x, y):
  return x*y
def frac(n):
  if n<=1:
    if n==0 or n==1:
      return 1
    else:
      print('n 不能小于0')
  else:
    return functools.reduce(fn, range(1, n+1))
  
print(frac(5))
print(frac(6))
print(frac(7))

# 使用 lambda 简写
import functools
def frac(n):
  if n<=1:
    if n==0 or n==1:
      return 1
    else:
      print('n 不能小于0')
  else:
    return functools.reduce(lambda x, y: x*y, range(1, n+1))
  
print(frac(5))
print(frac(6))
print(frac(7))

result = (lambda k: functools.reduce(int.__mul__, range(1, k + 1), 1))(5)
print(result)```

y = int(input("请输入要计算的数:"))
for i in range(1, y + 1):
x = x * i
print(x)

if n == 0 or n == 1:
return 1
else:
return (n * func(n - 1))
a = func(5)
print(a)