32. Valid Day

# -----------
# User Instructions
# 
# Modify the valid_day() function to verify 
# whether the string a user enters is a valid 
# day. The valid_day() function takes as 
# input a String, and returns either a valid 
# Int or None. If the passed in String is 
# not a valid day, return None. 
# If it is a valid day, then return 
# the day as an Int, not a String. Don't 
# worry about months of different length. 
# Assume a day is valid if it is a number 
# between 1 and 31.
# Be careful, the input can be any string 
# at all, you don't have any guarantees 
# that the user will input a sensible 
# day.
#
# Hint: The string function isdigit() might be helpful.

def valid_day(day):


# print valid_day('0') 
# => None    
# print valid_day('1') 
# => 1
# print valid_day('15') 
# => 15
# print valid_day('500') 
# => None

# -----------
# User Instructions
# 
# Modify the valid_day() function to verify 
# whether the string a user enters is a valid 
# day. The valid_day() function takes as 
# input a String, and returns either a valid 
# Int or None. If the passed in String is 
# not a valid day, return None. 
# If it is a valid day, then return 
# the day as an Int, not a String. Don't 
# worry about months of different length. 
# Assume a day is valid if it is a number 
# between 1 and 31.
# Be careful, the input can be any string 
# at all, you don't have any guarantees 
# that the user will input a sensible 
# day.
#
# Hint: The string function isdigit() might be helpful.

def valid_day(day):
    if day.isdigit():
        intday = int(day)
        if intday>0 and intday<32:
            return intday
        else:
            return None
    else:
        return None


print valid_day('0') 
# => None    
# valid_day('1') 
# => 1
print valid_day('15') 
# => 15
valid_day('500') 
# => None