Python 3阶乘

我正在学习python 3，现在我正在尝试实现我编写的阶乘函数：

fact = 1
a = input('Enter number for factorial operation: ')

for  b in range ( 1, a+1, 1 ):
    fact = fact * b

print ("Sum is ", fact)

它说：

 for  b in range ( 1, a+1, 1 ):
TypeError: Can't convert 'int' object to str implicitly

---

之所以会发生这种情况，是因为

input

返回的是

str

，而不是

int

，这正是您所追求的。您可以通过将

str

强制转换为

int

来修复此问题，如下所示：

a = int(input('Enter number for factorial operation: '))

看看这个：

In [68]: a = input('Enter number for factorial operation: ')
Enter number for factorial operation: 5

In [69]: a
Out[69]: '5'

In [70]: type(a)
Out[70]: str

In [71]: isinstance(a, str)
Out[71]: True

In [72]: isinstance(a, int)
Out[72]: False

In [73]: a = int(input('Enter number for factorial operation: '))
Enter number for factorial operation: 5

In [74]: a
Out[74]: 5

In [75]: type(a)
Out[75]: int

In [76]: isinstance(a, str)
Out[76]: False

In [77]: isinstance(a, int)
Out[77]: True

---

之所以会发生这种情况，是因为

input

返回的是

str

，而不是

int

，这正是您所追求的。您可以通过将

str

强制转换为

int

来修复此问题，如下所示：

a = int(input('Enter number for factorial operation: '))

看看这个：

In [68]: a = input('Enter number for factorial operation: ')
Enter number for factorial operation: 5

In [69]: a
Out[69]: '5'

In [70]: type(a)
Out[70]: str

In [71]: isinstance(a, str)
Out[71]: True

In [72]: isinstance(a, int)
Out[72]: False

In [73]: a = int(input('Enter number for factorial operation: '))
Enter number for factorial operation: 5

In [74]: a
Out[74]: 5

In [75]: type(a)
Out[75]: int

In [76]: isinstance(a, str)
Out[76]: False

In [77]: isinstance(a, int)
Out[77]: True

---

之所以会发生这种情况，是因为

input

返回的是

str

，而不是

int

，这正是您所追求的。您可以通过将

str

强制转换为

int

来修复此问题，如下所示：

a = int(input('Enter number for factorial operation: '))

看看这个：

In [68]: a = input('Enter number for factorial operation: ')
Enter number for factorial operation: 5

In [69]: a
Out[69]: '5'

In [70]: type(a)
Out[70]: str

In [71]: isinstance(a, str)
Out[71]: True

In [72]: isinstance(a, int)
Out[72]: False

In [73]: a = int(input('Enter number for factorial operation: '))
Enter number for factorial operation: 5

In [74]: a
Out[74]: 5

In [75]: type(a)
Out[75]: int

In [76]: isinstance(a, str)
Out[76]: False

In [77]: isinstance(a, int)
Out[77]: True

---

之所以会发生这种情况，是因为

input

返回的是

str

，而不是

int

，这正是您所追求的。您可以通过将

str

强制转换为

int

来修复此问题，如下所示：

a = int(input('Enter number for factorial operation: '))

看看这个：

In [68]: a = input('Enter number for factorial operation: ')
Enter number for factorial operation: 5

In [69]: a
Out[69]: '5'

In [70]: type(a)
Out[70]: str

In [71]: isinstance(a, str)
Out[71]: True

In [72]: isinstance(a, int)
Out[72]: False

In [73]: a = int(input('Enter number for factorial operation: '))
Enter number for factorial operation: 5

In [74]: a
Out[74]: 5

In [75]: type(a)
Out[75]: int

In [76]: isinstance(a, str)
Out[76]: False

In [77]: isinstance(a, int)
Out[77]: True

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