Python factorial()用法及代碼示例

沒有多少人知道，但是python提供了直接函數，可以計算數字的階乘而不用編寫用於計算階乘的整個代碼。

Naive method to compute factorial

# Python code to demonstrate naive method 
# to compute factorial 
n = 23
fact = 1
  
for i in range(1,n+1):
    fact = fact * i 
      
print ("The factorial of 23 is:",end="") 
print (fact)

輸出：

The factorial of 23 is:25852016738884976640000

Using math.factorial()

該方法在python的“math”模塊中定義。由於它具有C類型的內部實現，因此速度很快。

math.factorial(x)
參數：
x: The number whose factorial has to be computed.
返回值:
Returns the factorial of desired number.
異常:
Raises Value error if number is negative or non-integral.

# Python code to demonstrate math.factorial() 
import math 
  
print ("The factorial of 23 is:", end="") 
print (math.factorial(23))

輸出：

The factorial of 23 is:25852016738884976640000

Exceptions in math.factorial()

• 如果給定數字為負數：

  # Python code to demonstrate math.factorial() 
  # Exceptions ( negative number ) 
    
  import math 
    
  print ("The factorial of -5 is:",end="") 
    
  # raises exception 
  print (math.factorial(-5))

  輸出：

  The factorial of -5 is:
  

  運行時錯誤：

  Traceback (most recent call last):
    File "/home/f29a45b132fac802d76b5817dfaeb137.py", line 9, in 
      print (math.factorial(-5))
  ValueError:factorial() not defined for negative values
  

• 如果給定數字為非整數值：

  # Python code to demonstrate math.factorial() 
  # Exceptions ( Non-Integral number ) 
    
  import math 
    
  print ("The factorial of 5.6 is:",end="") 
    
  # raises exception 
  print (math.factorial(5.6))

  輸出：

  The factorial of 5.6 is:
  

  運行時錯誤：

  Traceback (most recent call last):
    File "/home/3987966b8ca9cbde2904ad47dfdec124.py", line 9, in 
      print (math.factorial(5.6))
  ValueError:factorial() only accepts integral values