Checking an input in python

Question

Basically, I'm asking for an input, which is going to be split(',') however, if the person doesn't input it properly, for example they accidentally input just 5, or don't include a comma at all, it comes up with an error that something is undefined.

Does anyone have any idea of how to check that the input is in the right sort of format?

Edit: Here's the code in question...it's to do with coordinates

def EnterCoords():
 coordinates = input("Enter coordinates in the following format x,y").split(',')
 x, y = Coordinates[0], Coordinates[1]

I then use the x and y values in a calculation elsewhere, which brings up the error IndexError: list index out of range So, if the user enters them wrong, is there a way of calling the function again, for them to try again

• Padraic Cunningham: show the actual error
• acrosman: Welcome to StackOverflow. You'll be much more likely to get a useful answer if you can include some code and the error you're seeing.
• James Taylor: I'm honestly sick of SO shutting down perfectly good questions. To OP: catch the ValueError. It's hard to know precisely if the text is formatted the way you want it until split() actually runs.
• Padraic Cunningham: are you using input or raw_input?
• Malik Brahimi: Instead of checking for a specific format, try searching for a specific values: data = raw_input('Enter a few values: ') # let's say 1, 3, 4.5, 5, nums = [] for entry in re.findall('[0-9.]+', data): nums.append(float(entry)) print nums # now just numbers regardless of commas

Answer 1

Given your updated question, then the best way is to use a try/except.

def enter_coords():
 while True:
 try:
 # Use `raw_input` for Python 2.x
 x, y = input('Enter coordinates ...: ').split(',')
 return int(x), int(y) # maybe use `float` here?
 except ValueError as e:
 pass

Keep looping until a successful return. By using x, y = - you're requesting that only two values should be unpacked (less or more will raise a ValueError), if that succeeds, then you try to return the int equivalent of those values, again, if they're not suitables ints, then you get a ValueError... you then ignore that error and the loop repeats until a successful return executes.

More general approaches and the principles of using this approach are detailed in the excellent: Asking the user for input until they give a valid response

• Padraic Cunningham: think you are missing a try :P
• Jon Clements: @Padraic looks embarrassed - thanks... still needed the while True there though :p
• Padraic Cunningham: ah fix one thing break another sounds familiar :)
• f.rodrigues: In python 3 there's the neat supress condtion, from contextlib import suppress with suppress(Exception): which will ignore the exception, it replaces the try/except: pass
• Jon Clements: @f.rodrigues it's a useful thing to know about, however in this case, it's not really applicable

Answer 2

Edit: Just realized you're not looking for alpha only string.

---

To check for commas use any of the following: There are multiple ways of solving this problem:

Using in operator

Check for a comma in the string using the in operator:

if "," in str:
 <code on true condition>

Example:

In [8]: if "," in "Hello World!":
 ...: print "Contains Comma"
 ...: 
In [9]: if "," in "Hello,World":
 ...: print "Contains Comma"
 ...: 
Contains Comma

-OR-

Exception Handling

You could use try ... except block to check for error when ',' is not present in string as suggested by James Taylor. See documentation for handling exceptions: https://docs.python.org/2/tutorial/errors.html#handling-exceptions

-OR-

RegEx

As suggested by Malik Brahimi in the comments - "Instead of checking for a specific format, try searching for a specific values":

data = raw_input('Enter a few values: ') # let's say 1, 3, 4.5, 5,
nums = []
for entry in re.findall('[0-9.]+', data):
 nums.append(float(entry))
print nums # now just numbers regardless of commas

• Manav Kataria: I believe regex is another valid way of solving the OP's problem. Your edit is worthy to be an independent answer. Kindly add one to augment the discussion.
• Malik Brahimi: I wasn't trying to be rude, the topic's been put on hold, and you seem to be accumulating downvotes. I thought my answer might be of use to you.
• Manav Kataria: Appreciate the clarification Malik, I will incorporate your answer. Secondly, that downvote was well deserved - due to misunderstanding of the OP's question which I've corrected since.
• Malik Brahimi: I didn't downvote you, don't be too hard on yourself.