AttributeError：'int'对象没有属性'isdigit'

Question

numOfYears = 0
cpi = eval(input("Enter the CPI for July 2015: "))
if cpi.isdigit():
    while cpi < (cpi * 2):
        cpi *= 1.025
        numOfYears += 1
    print("Consumer prices will double in " + str(numOfYears) + " years.")
while not cpi.isdigit():
    print("Bad input")
    cpi = input("Enter the CPI for July 2015: ")

I'm getting the following error.

AttributeError: 'int' object has no attribute 'isdigit'

Since I'm new to programming, I don't really know what it's trying to tell me. I'm using the if cpi.isdigit(): to check to see if what the user entered is a valid number.

Answer 1

As documented here isdigit() is a string method. You can't call this method for integers.

This line,

cpi = eval(input("Enter the CPI for July 2015: ")) 

evaluates the user input to integer.

>>> x = eval(input("something: "))
something: 34
>>> type(x)
<class 'int'>
>>> x.isdigit()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'isdigit'

But if you remove eval method (you should better do that),

>>> x = input("something: ")
something: 54
>>> type(x)
<class 'str'>
>>> x.isdigit()
True

everything will be fine.

by the way using eval without sanitizin user input may cause problems

consider this.

>>> x = eval(input("something: "))
something: __import__('os').listdir()
>>> x
['az.php', 'so', 'form.php', '.htaccess', 'action.php' ...

Answer 2

Use this:

if(str(yourvariable).isdigit()) :
    print "number"

isdigit() works only for strings.

Answer 3

numOfYears = 0
# since it's just suppposed to be a number, don't use eval!
# It's a security risk
# Simply cast it to a string
cpi = str(input("Enter the CPI for July 2015: "))

# keep going until you know it's a digit
while not cpi.isdigit():
    print("Bad input")
    cpi = input("Enter the CPI for July 2015: ")

# now that you know it's a digit, make it a float
cpi = float(cpi)
while cpi < (cpi * 2):
    cpi *= 1.025
    numOfYears += 1
# it's also easier to format the string
print("Consumer prices will double in {} years.".format(numOfYears))

Answer 4

eval() is very dangerous! And int() built-in function can convert string to digit.

If you want to catch the error if user didn't enter a number, just use try...except like this:

numOfYears = 0

while numOfYears == 0:
    try:
        cpi = int(input("Enter the CPI for July 2015: "))
    except ValueError:
        print("Bad input")
    else:
        while cpi < (cpi * 2):
            cpi *= 1.025
            numOfYears += 1

print("Consumer prices will double in", numOfYears, "years.")