Numeric comparison with user input always produces

问题:

I want to get a number input by the user via input() and compare it with a specific value, i.e., 3.

However, I have the impression my if statement doesn't work. The comparison is always False.

Start = input()
if Start == 3:
     print ("successful")

回答1:

Python 3 input function returns string.

Try like this

start = input("-->: ")
if start == "3":
    print("successful")

回答2:

Some things you could do on your own to get to the root of the problem:

Ways to get to know the type of the object:

print(type(start)) # prints <class 'str'>
print(repr(start)) # prints '3'

Unlike Python 2.x, the function input() returns a string object (and does not blindly evaluate the expression provided by the user):

input([prompt]):

If the prompt argument is present, it is written to standard output without a trailing newline. The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that. [...]

This should give an idea how to fix it (compare numbers to numbers).

For further reading:

• https://docs.python.org/3/library/functions.html#input
• https://docs.python.org/3/library/functions.html#type
• https://docs.python.org/3/library/functions.html#repr
• How does Python compare string and int?
• Asking the user for input until they give a valid response

回答3:

You can also try this as an alternative:

Adding int will convert the variable to int data type.

input = int(raw_input("Enter a num: "))
if input == 3:
   print "Successful"

回答4:

you should check your tabs (I recomend you to use four spaces, not regular tabs and not to mix them)

start = 0
start = input("-->:")
if start == "3":
    print("Success")