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.
4 Answers
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' ... Use this:
if(str(yourvariable).isdigit()) : print "number" isdigit() works only for strings.
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)) 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.") 
