Python: Compound Try/Except Blocks

Question

I am working on a random word picker (used in the command line). The word picker itself works perfectly (I have a text file that has a bunch of words separated by spaces. The program will take the text file and make a list, the entries being everything in the list split with spaces).

The next step I want to take is to be able to programmatically add words to the text file. I was able to get it to add whatever the user gives from input, but now I want to make sure that the word provided from the user doesn't have spaces, numbers, or uppercase letters.

The first attempt I took looked like this:

def add_word():
     word_to_add = input("Word to add: ")

     valid_word = False
     if any(char.isdigit() for char in word_to_add):
          valid_word = False
     elif any(char.isupper() for char in word_to_add):
          valid word = False
     elif any((" " in chars) for chars in word_to_add):
          valid word = False
     else:
          valid word = True

I know this is a super inefficient method to use. That said, I'm trying to use Try/Except blocks to clean it up a little bit. I think I have an idea of how they work. Since I'm trying to test against multiple conditions, it would be something like

try:
     # code for no numbers
try: 
     # code for no uppercases
try:
     # code for no spaces
except:
     # blah blah blah
else:
     # blah blah blah

Now, the dilemma I'm facing is how do I route each try: to a specific exception? What I mean is if there is an exception with the numbers, it would print something like "your word cannot contain numbers. Try again." and the same deal for spaces and uppercases: Is there a way for me to make something like this:

try:
     # if there's a number go to exception A
try:
     # if there's an uppercase go to exception B
try:
     # if there's a space go to exception C
exception a:
     # blah blah blah
exception b:
     # blah blah blah
exception c:
     # blah blah blah
else:
     # blah blah blah

Would it end up being more efficient to just have multiple try/except blocks or a "compound" version like the above code?

The reason I don't want to use if/elif/else is because sometimes it will still add the user input to the word list even if valid_word was false.

Sorry that I can't be more specific here, I just don't really know how to articulate what I'm trying to accomplish here. Thanks in advance for any help

Answer 1

You can raise an exception inside a try block to immediately jump to a matching except , eg:

def add_word():
    while True:
        word_to_add = input("Word to add: ")
        try:
            if any(char.isdigit() for char in word_to_add):
                raise ValueError("Your word cannot contain numbers!")
            if any(char.isupper() for char in word_to_add):
                raise ValueError("Your word cannot contain capitals!")
            if " " in word_to_add:
                raise ValueError("Your word cannot contain spaces!")
        except ValueError as err:
            print(err)
            print("Try again")
        else:
            break
    # now do whatever you need to do to add word_to_add

But you could just as easily structure this as an if/elif block where each error condition is an elif and you break the loop in the else :

def add_word():
    while True:
        word_to_add = input("Word to add: ")
        if any(char.isdigit() for char in word_to_add):
            print("Your word cannot contain numbers!")
        elif any(char.isupper() for char in word_to_add):
            print("Your word cannot contain capitals!")
        elif " " in word_to_add:
            print("Your word cannot contain spaces!")
        else:
            break
        print("Try again!")
    # now do whatever you need to do to add word_to_add

Answer 2

1. You can only have one try . But it can have multiple except s. You cannot stack multiple tries. You can legally try s inside each other just like you nest if statements or for loops. But there isn't much reason to do this in a single function since you can stack multiple except s on a single try .

2. The code in the except will only be called when some code raise s an error in the try . This most commonly happens when you call a function which then raises an error. But you can also manually raise in the try .