On Wed, Jul 1, 2020 at 6:23 AM Christopher Barker <python...@gmail.com> wrote:
> On Tue, Jun 30, 2020 at 8:55 PM David Lowry-Duda <da...@lowryduda.com> > wrote: > >> On the other hand, it seems far more likely to miss keys in a dictionary >> than it is to repeatedly mistake indices in a list. >> > > exactly -- dict keys are arbitrary, and it's pretty common to store > "sparse" data by simply leaving out the key if there's nothing interesting > attached to it. > > But for Sequences, the only time you get an index error is if you are > indexing beyond the length of the list, and the only case I can think of > for get() would be for a maybe-empty list. otherwise, would I really want > the same thing, and no error, for ANY index larger than the length of the > list? > > Rather, if there's a specific index we want, we want it to be there, and > if not, then we are iterating over it, which handles any length (including > zero) just fine. > > -CHB > dict.get is definitely much more useful. But list.get is still useful reasonably often. You can see quite a bit of demand for the method here: https://stackoverflow.com/questions/5125619/why-doesnt-list-have-safe-get-method-like-dictionary Below are some use cases I found and how they could be refactored with .get. Apart from the first one, they were all found simply by grepping for `except IndexError`. It's pretty easy to pick obvious use cases out from there. In some cases readability suffers a bit and using .get might not be the best idea, but I've included them anyway so that we can see what over-eager usage of the method might look like. ``` _pytest/_code/source.py if insert_index >= len(values): end = None else: end = values[insert_index] end = values.get(insert_index) -------------------- prompt_toolkit/layout/layout.py try: return self._stack[-2].content except IndexError: return self._stack[-1].content return self._stack.get(-2, self._stack[-1]).content -------------------- prompt_toolkit/buffer.py try: word = words[state.n] except IndexError: word = "" word = words.get(state.n, "") -------------------- prompt_toolkit/widgets/menus.py try: selected_item = self.selected_menu[level + 1] except IndexError: selected_item = -1 selected_item = self.selected_menu.get(level + 1, -1) -------------------- prompt_toolkit/document.py try: return self.text[self.cursor_position + offset] except IndexError: return "" return self.text.get(self.cursor_position + offset, "") -------------------- prompt_toolkit/contrib/regular_languages/lexer.py try: return lines[lineno] except IndexError: return [] return lines.get(lineno, []) -------------------- pip/_internal/cli/autocompletion.py try: subcommand_name = [w for w in cwords if w in subcommands][0] except IndexError: subcommand_name = None subcommand_name = [w for w in cwords if w in subcommands].get(0) -------------------- pip/_internal/cli/autocompletion.py try: current = cwords[cword - 1] except IndexError: current = '' current = cwords.get(cword - 1, '') -------------------- pip/_internal/configuration.py try: return self._get_parser_to_modify()[0] except IndexError: return None return self._get_parser_to_modify().get(0) -------------------- pip/_vendor/distlib/resources.py try: result = self.index[i].startswith(path) except IndexError: result = False result = self.index.get(i, "").startswith(path) -------------------- stack_data/core.py try: return not self.lines[i - 1].strip() except IndexError: return False return not self.lines.get(i - 1, "not blank").strip() -------------------- parso/tree.py try: return self.parent.children[i + 1] except IndexError: return None return self.parent.children.get(i + 1) -------------------- ipython/IPython/core/completer.py try: return self.matches[state] except IndexError: return None return self.matches.get(state) -------------------- ipython/IPython/core/magics/basic.py mode = '' try: mode = parameter_s.split()[0][1:] except IndexError: pass mode = parameter_s.split().get(0, '')[1:] -------------------- ipython/IPython/core/tests/simpleerr.py try: mode = sys.argv[1] except IndexError: mode = 'div' mode = sys.argv.get(1, 'div') -------------------- ipython/IPython/utils/text.py try: tgt = parts[field] return tgt except IndexError: return "" return parts.get(field, "") -------------------- py/_xmlgen.py try: tag.parent = self.parents[-1] except IndexError: tag.parent = None tag.parent = self.parents.get(-1, None) -------------------- ipython/IPython/core/tests/tclass.py try: name = sys.argv[1] except IndexError: pass else: if name.startswith('C'): c = C(name) name = sys.argv.get(1, "") if name.startswith('C'): c = C(name) ```
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