Programming Forums > Script Programming > Python

UnKnown X · Feb 11th, 2006, 2:09 PM

Using this code to get a sequence of 'words' (well, numbers, but that's irrelevant) separated by a space, it fails at the split(" ") when only one word is given (I assume). However, it doesn't raise an exception and I'm unsure on how to catch the single word anyway.

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def GetSequence(highNumber):
    while 1:
        sequence = GetString("Enter a Sequence of numbers separated by a space: ")
        try:
            list = []
            for word in sequence.split(" "):
                list.append(int(word))
        except ValueError:
            print "Error: '%s' is not a number! Try again." % word,
            continue
        except:
            print "Error! Try again.",
            continue
        break
    return list

UnKnown X · Feb 11th, 2006, 2:14 PM

Found a solution!

(Toggle Plain Text)

def GetSequence(highNumber):
    while 1:
        sequence = GetString("Enter a Sequence of numbers separated by a space: ")
        try:
            list = []
            try:
                list.append(int(sequence))
            except ValueError:
                for word in sequence.split(" "):
                    list.append(int(word))
            except:
                print "Error! Try again.",
                continue
        except ValueError:
            print "Error: '%s' is not a number! Try again." % word,
            continue
        except:
            print "Error! Try again.",
            continue
        break
    return list

I love quick fixes!

DaWei · Feb 11th, 2006, 2:21 PM

We appreciate your posting the solution for other people. All too often people don't do that, or destroy their post, or something. Thanks.

UnKnown X · Feb 11th, 2006, 2:24 PM

Glad to help! (Even though I probably mostly helped myself here...

)

hydroxide · Feb 11th, 2006, 11:28 PM

Quote:

Originally Posted by UnKnown X

Using this code to get a sequence of 'words' (well, numbers, but that's irrelevant) separated by a space, it fails at the split(" ") when only one word is given (I assume). However, it doesn't raise an exception and I'm unsure on how to catch the single word anyway.

Your problem is elsewhere - it's perfectly ok to split on a non-existent token:

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x = "1234"
print x.split(" ")  # Will be a single-element list.

The "GetString" is the likely culprit. Instead of hand-rolling your own, just use raw_input():

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def get_sequence():
    while True:
        seq = raw_input("Enter a sequence of numbers separated by a space: ")
        try:
            return [int(word) for word in seq.split(" ")]
        except ValueError:
            print "Error: '%s' is not a number! Try again." % word
print get_sequence()

reasons for some of the other changes:
* functions and variables use lower_case; classes use MixedCase.
* high_number was unused
* "while True" is a little prettier than while 1
* It's easier to build a list comprehension than manually create and append elements.
* Never call a list "list" since it shadows a built-in.
* The only exception that the return... line is likely to raise is ValueError. Any other exception is a critical one (eg: MemoryError, in which case continuing is not a great idea)
* bare excepts shouldn't be used in 99% of cases.

-T.

UnKnown X · Feb 12th, 2006, 4:39 AM

Thanks for your post, hydroxide!

I don't think Get_string is doing anything wrong - it does use raw_input, just with error checking. I just put it in a separate function to keep it a bit neat.

Here it is anyway:

(Toggle Plain Text)

def Get_sequence():
    while True:
        sequence = Get_string("Enter a Sequence of numbers separated by a space: ")
        if sequence == None:
            return None
        try:
            token_list = []
            try:
                token_list.append(int(sequence))
            except ValueError:
                for word in sequence.split(" "):
                    token_list.append(int(word))
            except:
                print "Error! Try again.",
                return None
        except ValueError:
            print "Error: '%s' is not a number! Try again." % word,
            continue
        except:
            print "Error!",
            return None
        break
    return token_list

def Get_string(msg):
    while True:
        try:
            return raw_input(msg)
        except ValueError:
            print "ValueError exception encountered! Try again."
            continue
        except:
            print "Error!"
            return None
        break
    print "Loop error occured!"
    return None

Arevos · Feb 12th, 2006, 5:14 AM

Quote:

Originally Posted by UnKnown X

I don't think Get_string is doing anything wrong - it does use raw_input, just with error checking. I just put it in a separate function to keep it a bit neat.

Generally speaking, it's okay if a function raises an exception - that's what they're there for - just so long as the exception is eventually caught. It's also worth thinking about dividing your program in generalised pieces:

(Toggle Plain Text)

def parse_sequence(sequence):
    output = []
    for item in sequence.split(" "):
        try:
            output.append(int(item))
        except ValueError:
            raise ValueError, "'%s' is not a number! Try again." % item
    return output

def get_user_sequence(prompt):
    return parse_sequence(raw_input(prompt))

def printer(s):
    print s

def while_exceptions(function, logger = printer):
    while True:
        try:
            return function()
        except Exception, e:
            logger(e)

def main():
    def get_sequence():
        return get_user_sequence(
                "Enter a sequence of numbers separated by a space: ")
    print while_exceptions(get_sequence, printer)

main()

Feb 11th, 2006, 2:09 PM	#1
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Catching only one word Using this code to get a sequence of 'words' (well, numbers, but that's irrelevant) separated by a space, it fails at the split(" ") when only one word is given (I assume). However, it doesn't raise an exception and I'm unsure on how to catch the single word anyway. (Toggle Plain Text) def GetSequence(highNumber): while 1: sequence = GetString("Enter a Sequence of numbers separated by a space: ") try: list = [] for word in sequence.split(" "): list.append(int(word)) except ValueError: print "Error: '%s' is not a number! Try again." % word, continue except: print "Error! Try again.", continue break return list def GetSequence(highNumber): while 1: sequence = GetString("Enter a Sequence of numbers separated by a space: ") try: list = [] for word in sequence.split(" "): list.append(int(word)) except ValueError: print "Error: '%s' is not a number! Try again." % word, continue except: print "Error! Try again.", continue break return list Last edited by UnKnown X; Feb 11th, 2006 at 2:17 PM. Reason: Typo

Feb 11th, 2006, 2:14 PM	#2
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Found a solution! (Toggle Plain Text) def GetSequence(highNumber): while 1: sequence = GetString("Enter a Sequence of numbers separated by a space: ") try: list = [] try: list.append(int(sequence)) except ValueError: for word in sequence.split(" "): list.append(int(word)) except: print "Error! Try again.", continue except ValueError: print "Error: '%s' is not a number! Try again." % word, continue except: print "Error! Try again.", continue break return list def GetSequence(highNumber): while 1: sequence = GetString("Enter a Sequence of numbers separated by a space: ") try: list = [] try: list.append(int(sequence)) except ValueError: for word in sequence.split(" "): list.append(int(word)) except: print "Error! Try again.", continue except ValueError: print "Error: '%s' is not a number! Try again." % word, continue except: print "Error! Try again.", continue break return list I love quick fixes!

Feb 11th, 2006, 2:21 PM	#3
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	We appreciate your posting the solution for other people. All too often people don't do that, or destroy their post, or something. Thanks. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Feb 12th, 2006, 4:39 AM	#6
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Thanks for your post, hydroxide! I don't think Get_string is doing anything wrong - it does use raw_input, just with error checking. I just put it in a separate function to keep it a bit neat. Here it is anyway: (Toggle Plain Text) def Get_sequence(): while True: sequence = Get_string("Enter a Sequence of numbers separated by a space: ") if sequence == None: return None try: token_list = [] try: token_list.append(int(sequence)) except ValueError: for word in sequence.split(" "): token_list.append(int(word)) except: print "Error! Try again.", return None except ValueError: print "Error: '%s' is not a number! Try again." % word, continue except: print "Error!", return None break return token_list def Get_string(msg): while True: try: return raw_input(msg) except ValueError: print "ValueError exception encountered! Try again." continue except: print "Error!" return None break print "Loop error occured!" return None def Get_sequence(): while True: sequence = Get_string("Enter a Sequence of numbers separated by a space: ") if sequence == None: return None try: token_list = [] try: token_list.append(int(sequence)) except ValueError: for word in sequence.split(" "): token_list.append(int(word)) except: print "Error! Try again.", return None except ValueError: print "Error: '%s' is not a number! Try again." % word, continue except: print "Error!", return None break return token_list def Get_string(msg): while True: try: return raw_input(msg) except ValueError: print "ValueError exception encountered! Try again." continue except: print "Error!" return None break print "Loop error occured!" return None

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Feb 11th, 2006, 2:24 PM	#4
UnKnown X Hobbyist Programmer Join Date: Dec 2005 Location: Sandvika, Norway Posts: 114 Rep Power: 0	Glad to help! (Even though I probably mostly helped myself here... )

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Programming Forums > Script Programming > Python

Catching only one word