Why does my string remove multiple characters? [duplicate]

Question

I've noticed a very curious phenomenon here. I've instantiated a global variable (usrPIN), and I'm comparing it to a local variable (c). When I input a value (in this case, four zeros), the value is chopped off, creating a string that is one character long. Why?

usrPIN
...
def login():
    global usrPIN
    ...
    c = str(input("Enter PIN"))
    print usrPIN
    print str(c)
    if usrPIN == c:
        mainMenu()
    else:
        print "Incorrect PIN"
        login()

What on earth is going on?

Use raw_input(...) rather than str(input(...)) - str(eval(raw_input('0000'))) is effectively str(int('0000')), which is '0'. Also, while you're here: don't use globals. — jonrsharpe
– jonrsharpe, Commented Oct 22, 2015 at 15:24
@jonrsharpe You were correct. Additionally, whilst I've read about globals being somewhat dangerous, I have multiple functions that I'm passing these variables to. Using globals is the most logical solution I've found so far - I've only been learning Python for two days. — Wolfish
– Wolfish, Commented Oct 22, 2015 at 15:55

Dylan Lawrence · Accepted Answer · 2015-10-22 15:33:55Z

3

In Python 2.x input() does automatic evaluation. What this means is when I do:

input(0.2757)

Python evaluates that to be a float. Similarly, in your case 0000 is evaluated as an integer and since four zeros is the same as one zero, it chops those away. In Python 2.x it's generally always recommended to use raw_input() for safety.

Note: raw_input() in Python 2.x always returns a string.

edited Oct 22, 2015 at 15:33

answered Oct 22, 2015 at 15:27

Dylan Lawrence

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2 Comments

Wolfish Over a year ago

This was the one - OOI, why does this occur even if I specify str()? Is it because the implicit conversion happens before the specification?

Dylan Lawrence Over a year ago

@Wolfish Internally input() looks kind of like eval(raw_input()) so when you say str(input()) you're actually saying str(eval(raw_input())) so the evaluation has already occurred before you ask for a string conversion.

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