python exit loop by 'enter'

sycamorex · 08-27-2008, 03:39 PM

hi,

I want the user to enter integers as long as they want (and append them to the list), however, once you just press enter (without any integer) the program should go out of the loop to e.g. some other function.
So far I've written the following:

Code:

marks = []
single_mark = 1

while single_mark != " ":
    single_mark = int(raw_input("enter your mark: "))
    marks.append(single_mark)

Code:

while single_mark != " ";

was supposed to mean 'continue the loop until the user's input is not just 'enter' - It doesn't work as I meant it to work.

Any hints, thanks

ntubski · 08-27-2008, 05:14 PM

You set single_mark to be the result of int(), so there is no way it could ever be equal to " " or any other string. You need to test the returned value of raw_input against "" (not " ").

osor · 08-27-2008, 05:41 PM

Two things:

Pressing enter ('') is not the same as typing a space and pressing enter (' ').
You cannot (without exception handling) int() a non-numerical string (and '' happens to be a non-numerical string).

Here’s what I might do (if you want to avoid exception handling):

Code:

while True:
    single_mark = raw_input("enter your mark: ")
    if single_mark == '':
        break
    marks.append(int(single_mark))

sycamorex · 08-28-2008, 02:56 PM

hi, thanks for your replies.

I completed what I wanted:

Code:

#!/usr/bin/env python

marks = []
sum = 0

while True:
    single_mark = raw_input("enter your mark: ")
    if single_mark == '':
        break
    elif int(single_mark) > 6:
        print "The mark scale is 2-6"
    elif int(single_mark) < 2:
        print "The mark scale is 2-6"
    else:
        marks.append(int(single_mark))
        print "The mark has been added to the database"


print "You entered %d marks" % len(marks)
print "Your marks are as follows: "
x = 0
for x in marks:
    print x
    sum += x

average = float(sum) / len(marks)

print "Your average mark is %f" % average

I'm a python beginner so can you tell me what you would improve in this simple code?

thanks

osor · 08-28-2008, 06:13 PM

Quote:

Originally Posted by sycamorex

I'm a python beginner so can you tell me what you would improve in this simple code?

A few things:

You shouldn’t need to pre-declare x.
Since the second and third conditionals have an identical “THEN” block, you can combine them with a logical OR.
You are calling int(single_mark) three times. The python interpreter will (or should) optimize this into a single call whose result is kept in a register, but you can’t always count on the interpreter to clean up your inefficiencies.
Stylistically, you can separate the second and third conditionals (which should be combined as stated above) into their own if (there is no need for elif since a break effectively ends that code pathway).

Shadowmeph · 08-29-2008, 05:15 PM

Quote:

Originally Posted by sycamorex

hi, thanks for your replies.

I completed what I wanted:

Code:

#!/usr/bin/env python

marks = []
sum = 0

while True:
    single_mark = raw_input("enter your mark: ")
    if single_mark == '':
        break
    elif int(single_mark) > 6:
        print "The mark scale is 2-6"
    elif int(single_mark) < 2:
        print "The mark scale is 2-6"
    else:
        marks.append(int(single_mark))
        print "The mark has been added to the database"


print "You entered %d marks" % len(marks)
print "Your marks are as follows: "
x = 0
for x in marks:
    print x
    sum += x

average = float(sum) / len(marks)

print "Your average mark is %f" % average

I'm a python beginner so can you tell me what you would improve in this simple code?

thanks

I am interested in Learning python I am wondering where are you learning this?

rocket357 · 08-29-2008, 05:57 PM

Quote:

Originally Posted by Shadowmeph

I am interested in Learning python I am wondering where are you learning this?

There are a ton of great sites out there for python...

http://www.python.org (check out the Tutor mailing list...it's active and the people there are quite friendly...)
http://www.uselesspython.com/tutorials.php

Most Linux distributions have a package of "Dive Into Python", a great ebook on Python (or you can get it here: http://www.diveintopython.org/)

Numerous Python books:
Learning Python
Python in a Nutshell
etc...

Shadowmeph · 08-29-2008, 09:44 PM

Quote:

Originally Posted by rocket357

There are a ton of great sites out there for python...

http://www.python.org (check out the Tutor mailing list...it's active and the people there are quite friendly...)
http://www.uselesspython.com/tutorials.php

Most Linux distributions have a package of "Dive Into Python", a great ebook on Python (or you can get it here: http://www.diveintopython.org/)

Numerous Python books:
Learning Python
Python in a Nutshell
etc...

Thanks I will check those out