Creating Python class with regular expressions

Question

I apologize for the newbie question, but this is my first time working with classes. The class I'm trying to create is intended to perform a regex find and replace on all keys and values within a dictionary. The specific find and replace is defined upon instantiation.

There are two issues that I have. The first issue is that each instance of the class needs to accept a new dictionary. I'm not clear on how to create a class that accepts a general dictionary which I can specify upon creating an instance. The second issue is that the class I have simply isn't working. I'm receiving the error message TypeError: expected string or buffer in the class line v = re.sub(self.find,self.replace,v).

There are three instances I want to create, one for each input dictionary: input_iter1, input_iter2, and input_iter3.

The following is the class:

class findreplace:
    values = []
    keys = []
    def __init__(self, find, replace):
        self.find = find
        self.replace = replace
    def value(self):
        for k,v in input_iter1.items():
            v = re.sub(self.find,self.replace,v)
            findreplace.values.append(v)
    def key(self):
        for k,v in input_iter1.items():
            k = re.sub(self.find,self.replace,k)
            findreplace.keys.append(k)

The following are the instances:

values1 = findreplace('[)?:(]','')
values1.value()
values2 = findreplace(r'(,\s)(,\s)(\d{5})({e<=1})',r'\2\3')
values2.value()
keys1 = findreplace(r'(?<=^)(.+)(?=$)',r'(?:\1)')
keys1.key()
keys2 = findreplace(r'(?=$)',r'{e}')
keys2.key()

print values
print keys

If anyone has any insight on how I can workaround these two issues, I'd be grateful to hear them. Thanks!

Eevee · Accepted Answer · 2013-01-21 05:11:50Z

2

First, Python 2 classes should start off this way:

class Foo(object):

Otherwise, you get an "old-style class", which is some ancient crusty thing no one uses.

Also, class names in Python are typically written in CamelCase.

Second, do not use mutable values (like lists!) as class attributes, as you're doing here with keys and values. They'll be shared across all instances of your class! It looks like you're even aware of this, since you refer to findreplace.keys directly, but it doesn't make sense to store instance-specific values in a class attribute like that.

But, most importantly: why is this a class at all? What does a findreplace represent? It looks like this would be much clearer if it were just a single function.

To answer your actual questions:

You pass in a dictionary just like you're passing in find and replace. Add another argument to __init__, and pass another argument when you construct your class.
Presumably, you're getting the TypeError because one of the values in your dictionary isn't a string, and you can only perform regexes on strings.

answered Jan 21, 2013 at 5:11

Eevee

48.7k11 gold badges100 silver badges128 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

baobobs Over a year ago

I thought a creating a class may be better because it would otherwise get exceedingly verbose, but if you think I would be better off simply using functions, I'll take that as an acceptable answer. Thanks for the detailed reply.

Eevee Over a year ago

as a rule of thumb, if i can't explain to someone else what an instance of some class is (not "does"!) in ten words or fewer, it shouldn't be a class :) a lot of awkward classes force me to start off with "it's an object that..." which uses up most of my words already

user2665694 · Accepted Answer · 2013-01-21 05:10:38Z

1

Where is your definition of the input_iter dicts? How do they look like? Your error indicates that the values of your dicts are not strings.

answered Jan 21, 2013 at 5:10

user2665694

Collectives™ on Stack Overflow

Creating Python class with regular expressions

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related