scanning user input in python

Question

direction = input("enter a direction: ")
if direction != "quit" and direction != "go north" and direction != "go south" and direction != "go east" and direction != "go west" and direction != "go up" and direction != "go down" and direction != "look":
    print ("please enter in the following format, go (north,east,south,west,up,down)")

elif direction == "quit":
    print ("OK ... but a small part of you may never leave until you have personally saved Muirfieland from the clutches of evil .. Bwahahahahahah (sinister laugh) ... the game should then end.")

elif direction == "look":
    print ("You see nothing but endless void stretching off in all directions ...")

else:
    print ("You wander of in the direction of " + direction)

i need to know how to do this in python. i need to scan user inputs first 2 letters for example

i = user_input
#user inputs go ayisgfdygasdf

i need it to be able to scan the user input, check if the first 2 letters are go, and if they are go but it doesnt recognise the second word which in this case is "ayisgfdygasdf" then to print "sorry, i cant do that"

not really, if the program recognises the first word which is "go" but doesnt recognise the second word then python prints "sorry, i cant do that" — user2232076
– user2232076, Commented Apr 1, 2013 at 23:08

Disconnect3d · Accepted Answer · 2013-04-01 23:14:18Z

1

He could also try using:

    directions.split()

But it may require to use try/except in some cases.

For more information about split and methods try using:

    dir(directions)

to see what methods object directions have

or:

    help(directions.split)

to see help about a specific method (in this case method split of object directions)

answered Apr 1, 2013 at 23:14

Disconnect3d

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1 Comment

Karl Knechtel Over a year ago

.split() itself will always work as long as directions actually is a string; no need to catch exceptions there. However, you do then need to worry about how many items are in the result :)

e.beyer · Accepted Answer · 2013-04-01 23:09:11Z

0

You can access characters of a string in python by index using the [] notation. You can check the first two character in a string by typing user_input[:2]. This code will include all characters up to, but not including the index typed. So this notation will include user_input[0] and user_input[1]. You can then check if user_input[:2] is equal to 'go' or not, and continue from there.

Hope this helped.

answered Apr 1, 2013 at 23:09

e.beyer

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3 Comments

user2232076 Over a year ago

i got this to work, but i got another problem if you look at my code for example if user input is "go north" it will print "you wonder off in the direction of go north" i would like to remove the "go " from the user input, how would i do this?

Juan Carlos Moreno Over a year ago

use this direction[3:] for printing, this will use a subarray from the third character on.

e.beyer Over a year ago

that's correct, user_input[3:] will contain the substring from character 3 to end of string (in this example, it would include the space character) user_input[4:] would exclude the space character if that's what you wanted.

Juan Carlos Moreno · Accepted Answer · 2013-04-01 23:10:06Z

0

Instead try using:

direction = sys.stdin.readlines()

It may require you to ctrl+D after you are done but you will be able to capture so much more.

Also, to get the subarray you can then you can even check:

direction[:2] != "go"

or alternatively, for more readable code:

if not direction.startswith("go"):

Also I'd recommend, for making your code more readable,

defined_direction = frozenset(["quit", "go north", "go south"])
if( direction not in defined_direction):
   print "please enter...."

answered Apr 1, 2013 at 23:10

Juan Carlos Moreno

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2 Comments

Juan Carlos Moreno Over a year ago

No prob, I just answered on another comment that you still had a question about using the last item of the "go ". Let me know if that answer is clear. :)

abarnert Over a year ago

What exactly does sys.stdin.readlines() get you that sys.stdin doesn't? Or, for that matter, calling input in a loop? Other than the downside that it requires you to hit ^D after you're done, or ^Z on Windows, and it may not work with some IDEs, and so on?

dckrooney · Accepted Answer · 2013-04-01 23:27:37Z

You can index the individual characters of your input:

if direction[:2] == "go":
    print "Sorry, I can't do that."

However, trying assign an if-else branch to each possible input is typically a bad choice... It becomes difficult to maintain very quickly.

A cleaner approach in this case might be to define a dictionary with valid input as follows:

input_response = {"quit":"OK ... but", "go north": "You wander off north", \
                  "go south": "You wander off south"} # etc

You could then re-write your code to something like:

try:
    print input_response[direction]
except KeyError:
    if direction[:2] == "go":
        print "Sorry, I can't do that."
    else:
        print ("please enter in the following format...")

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