Question

I have the following snippet:

def check1(n):
    if len(n) != 4:
        return raw_input("Enter 4 digits only")
    else:
        return True

def check2(n):
    if n.isdigit() != True:
        return raw_input("Enter digits only")
    else:
        return True

def check3(n):
    if len(set(str(n))) != 4:
        return raw_input("Enter non duplicate numbers only")
    else:
        return True

sturn = 1
lturn = 8       

a = raw_input("Enter the 4 numbers you want to play with: ")

for turn in range(sturn, lturn):
    b = raw_input("Enter your guess: ")
    if (check1(b) != True or check2(b) != True or check3(b) != True):
        if check1(b) != True:
            print check1(b)
        elif check2(b) != True:
            print check2(b)
        elif check3(b) != True:
            print check3(b)
    else:
        print b

How can I rewrite this such that if any of the check functions fail, it starts from the b = raw_input line again and retests all the checks.

UPDATE
I’ve improved the code after heeding the advice from keithjgrant and m1k3y02 but it doesn’t work properly. If I enter ‘1’ consecutively, it bounces between different exceptions instead of staying on the first check.

def checks(n):
    if len(n) != 4 or n.isdigit() != True or len(set(str(n))) != 4:
        return False
    else:
        return True

sturn = 1
lturn = 8       

a = raw_input("Enter the 4 numbers you want to play with: ")

for turn in range(sturn, lturn):
    b = raw_input("Enter your guess: ")
    while checks(b) != True:
        if len(b) != 4:
            b = raw_input("Enter 4 digits only")
        if b.isdigit() != True:
            b = raw_input("Enter digits only")
        if len(set(str(b))) != 4:
            b = raw_input("Enter non duplicate numbers only") 

    print b

Answer 1

Your question, as it stands, has nothing to do with exceptions. Try the following:

checks = [
    lambda n: (len(n)==4, "Enter 4 digits only."),
    lambda n: (n.isdigit(), "Enter digits only."),
    lambda n: (len(set(str(n)))==4, "Enter non duplicate numbers only.")
]

a = raw_input("Enter the 4 numbers you want to play with: ")

sturn = 1
lturn = 8
for turn in range(sturn, lturn):
    b = raw_input("Enter your guess: ")
    all_good = True

    for check in checks:
        good,msg = check(b)
        if not good:
            print msg
            all_good = False
            break

    if all_good:
        print "{0} is correct!".format(b)
        break

You could rewrite it to use exceptions as follows:

class CheckError(Exception): pass

class WrongLengthError(CheckError): pass
def check1(n):
    if len(n) != 4:
        raise WrongLengthError("Enter 4 digits only.")

class NonDigitCharError(CheckError): pass
def check2(n):
    if not n.isdigit():
        raise NonDigitCharError("Enter digits only.")

class HasDuplicatesError(CheckError): pass
def check3(n):
    if len(set(str(n))) != 4:
        raise HasDuplicatesError("Enter non duplicate numbers only.")


a = raw_input("Enter the 4 numbers you want to play with: ")

sturn = 1
lturn = 8
for turn in range(sturn, lturn):
    b = raw_input("Enter your guess: ")

    try:
        for check in (check1, check2, check3):
            check(b)

        print "{0} is correct!".format(b)
        break
    except CheckError, c:
        print c