CODEWITHSUNDEEP
pythonstringlist
user14177981
user14177981

Reputation:

How to see if a string is written in a specific form

I'm trying to write this code, where a program takes the input in the form: (x - / + y)(x / + y)

I've come this far (ignore the prints as it's written in swedish):

user_input = list(input('Skriv ett tal på formen (x +/- y)(x +/- y): '))
operator_list = []


for i in range(len(user_input)):
    if user_input[i] == '-' or user_input[i] == '+':
        operator_list.append(i)

def method():
    if user_input[operator_list[0]] == '-' and user_input[operator_list[1]] == '-':
        return('2:a kvadreringsregeln')

    elif user_input[operator_list[0]] == '+' and user_input[operator_list[1]] == '+':
        return('1:a kvadreringsregeln')

    elif user_input[operator_list[0]] != user_input[operator_list[1]]:
        return('Konjugatregeln')

print('Ditt tal:', ''.join(user_input), 'är skriven enligt:', method())

However right now the program doesn't require the user to input it with any parenthesis, or in any particular order,

i.e the input can be:

(-- or (          -a)(+

etc.

However I want to user to only be able to input the code in this form:

(x -/+ y)(x -/+ y) or (x-/+y)(x-/+y) or (x -/+y)( x -/+y)

With spaces being of no importance

I was thinking of using the python import regex but I don't know how it works so help would be appreciated :D

Upvotes: 0

Views: 194

Answers (2)

Kilian
Kilian

Reputation: 579

You can do a Regex with re package with the match function :

import re

input = "(x  +/-y)(x+/-y )"
pattern = "\(x\+/-y\)\(x\+/-y\)"

if re.match(pattern, input.lstrip()) is not None:
    print("your input is on the correct format")
else:
    print("your input is not correct")

Note that the \ character escape special characters (like "()" or "+", ect...). Also, the .lstrip() function removes all white space in your string.

Here, the pattern match x and y as characters, but if you want to check them as integer, your pattern would look like this : "\(\d+\+/-\d+\)\(\d+\+/-\d+\)".

The \d+ check if the string contains 1 or more digits (between 0 and 9).

For more information about Regex in Python, you can have a look at the w3school website.

EDIT :

If you want to include variable like 43x, 4y... you can do that with the following pattern : "\(\d+\D*\+/-\d+\D*\)\(\d+\D*\+/-\d+\D*\)" with \D* zero or more string that DOES NOT contain digits.

Upvotes: 0

Myccha
Myccha

Reputation: 1018

Yes, regex is the right idea. You basically want to write a regular expression that will only match the text you consider "good".

To give a very quick overview of regex, if you write r"\d+[A-Z][a-z]*" that would only match strings that start with one or more digits \d+, followed by an uppercase letter [A-Z], followed by a lowercase letter [a-z], and ending with whatever *.

Your use case sounds complicated, but let me try:

import re
pattern = r'\(\w+[+|-]\w+\)\(\w+[+|-]\w+\)'

def test_match(pattern):
    
    assert re.match(pattern, '(x+y)(x+y)')
    assert re.match(pattern, '(x+y)(x-y)')
    assert re.match(pattern, '(x-y)(x+y)')
    assert re.match(pattern, '(x-y)(x-y)')
    assert re.match(pattern, '(a-b)(c-d)')

    assert not re.match(pattern, '(x?y)(x-y)')
    assert not re.match(pattern, '(x-y(x-y)')
    assert not re.match(pattern, '(x-y)(x--y)')

test_match(pattern)

And then you could validate your input by doing

if re.match(pattern, input_text.replace(' ',''):
   ...

Do you need x & y to be the only valid inputs for the variables?

Upvotes: 1

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