Using eval() in python to add numbers

Question

I want to let user enter string such as 2+5-3+6 and return 10. If user enter c then answer will be printed. I don't know how to make the project break when user enter a c.

print 'This is a calculator. Please follow the instruction.'

temp = 0
string = 0

def asmd(string):
    print 'Your answer is', eval(str(string))

while temp != 'c':
    print 'Please enter a number or operation. Enter c to complete. :'
    temp = raw_input()
    string = str(string)+str(temp)

    if temp == str('c'):
        asmd(string)

eval is dangerous, it can easily be used to inject code into your script for undesired consequences. see stackoverflow.com/questions/1826859/… — Inbar Rose
– Inbar Rose, Commented Oct 18, 2012 at 16:45
@InbarRose: Good article by Ned Batchelder on the topic: nedbatchelder.com/blog/201206/eval_really_is_dangerous.html — Joel Cornett
– Joel Cornett, Commented Oct 18, 2012 at 16:46

jsalonen · Accepted Answer · 2012-10-18 17:02:16Z

1

To fix the calculator, just make sure the ending character (c) doesn't end up in your result string:

if temp == str('c'):
    asmd(string[:-1])

I have to note though that the whole script is pretty crazy. You are using eval, which can evaluate complete expressions at once, but still you instruct users to enter them one-by-one. With eval, you can rewrite your whole script in one line:

print eval(raw_input())

Also as extensively pointed out in the comments, it is generally bad idea to use eval in case you don't trust the user running your calculator. If you are just practising then fine -- just don't use eval in "real code".

edited Oct 18, 2012 at 17:02

answered Oct 18, 2012 at 16:49

jsalonen

30.8k15 gold badges93 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

hitheredude Over a year ago

Thanks. I wanted to practice how to end the calculation if user enter a 'c'.

jsalonen Over a year ago

Yeah. If so then you just need to remove the c character from your string as stated above. Otherwise you get like 1+2c which has a syntax error.

Collectives™ on Stack Overflow

Using eval() in python to add numbers

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related