[Python-Dev] PEP for Better Control of Nested Lexical Scopes (original) (raw)

Steven Bethard steven.bethard at gmail.com
Tue Feb 21 22:47:42 CET 2006

On 2/21/06, Josiah Carlson <jcarlson at uci.edu> wrote:

The question which still remains in my mind, which I previously asked, is whether the use cases are compelling enough to warrant the feature addition.

I don't know whether I support the proposal or not, but in reading Mark Russel's email, I realized that I just recently ran into a use case:

group tokens into chunks by their chunk labels

token_groups = [] curr_suffix = '' curr_tokens = [] for token in document.IterAnnotations('token', percent=80): label = token[attr_name]

# determine the prefix and suffix of the label
prefix, suffix = label[0], label[2:]

# B labels start a new chunk
if prefix == 'B':
    curr_suffix = suffix
    curr_tokens = [token]
    token_groups.append((curr_suffix, curr_tokens))

# I labels continue the previous chunk
elif prefix == 'I':
    if curr_suffix == suffix:
        curr_tokens.append(token)
    # error: change in suffix - this should be a B label
    else:
        # log the error
        message = '%r followed by %r'
        last_label = curr_tokens[-1][attr_name]
        self._logger.info(message % (last_label, label))
        # start a new chunk
        curr_suffix = suffix
        curr_tokens = [token]
        token_groups.append((curr_suffix, curr_tokens))

# O labels end any previous chunks
elif prefix == 'O':
    curr_suffix = suffix
    curr_tokens = [token]

You can see that the code::

    curr_suffix = suffix
    curr_tokens = [token]
    token_groups.append((curr_suffix, curr_tokens))

is repeated in two places. I would have liked to factor this out into a function, but since the code requires rebinding curr_suffix and curr_tokens, I can't. I'm not sure I care that much -- it's only three lines of code and only duplicated once -- but using something like curr_suffix := or Phillip J. Eby's suggestion of .curr_suffix = would allow this code to be factored out into a function.

STeVe

Grammar am for people who can't think for myself. --- Bucky Katt, Get Fuzzy

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