Re: How to tell if function was passed a list or a string?
Roy Smith wrote: Ben Finney [EMAIL PROTECTED] wrote: Currently there's no good duck-typing way to differentiate strings from other sequences. I suppose you could do something like: try: foo.isalpha except AttributeError: print foo is not a string Another way: if getattr (foo, 'isalpha', False): print 'foo is a string' Of course now string duck types must have an 'isalpha' and list ones can't, but that shouldn't matter much. -- Edward Elliott UC Berkeley School of Law (Boalt Hall) complangpython at eddeye dot net -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
import types type() is types.ListType False type() is types.StringType True type([]) is types.StringType False type([]) is types.ListType True This is even worse than an 'isinstance' check; it refuses even subclasses of the types you accept, breaking polymorphism *and* inheritance. And also note the following comment in the types module of the standard library that was imported above: # StringTypes is already outdated. Instead of writing type(x) in # types.StringTypes, you should use isinstance(x, basestring). But # we keep around for compatibility with Python 2.2. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
rh0dium [EMAIL PROTECTED] wrote: [ ... ] Since you have lots of answers to your real question: an.append(re.sub(,,, str(a))) an.append(str(a).replace(,, )) -- \S -- [EMAIL PROTECTED] -- http://www.chaos.org.uk/~sion/ ___ | Frankly I have no feelings towards penguins one way or the other \X/ |-- Arthur C. Clarke her nu becomeþ se bera eadward ofdun hlæddre heafdes bæce bump bump bump -- http://mail.python.org/mailman/listinfo/python-list
How to tell if function was passed a list or a string?
Hi All, I have the nice little function (below) which used to work great assuming the data[key] passed to it was a list. Well now I want to update this a bit. I want this function to be smart enough to tell if it's a list and do the funky concatonation otherwise don't. def insert(self, table=None, data=None): insert1=[] insert2=[] for key in data.keys(): insert1.append(key) self.logger.debug(Key: %s Data: %s % ( key,data[key])) try: an = [] for a in data[key]: an.append(re.sub(,,, str(a))) ans = string.join(an, , ) except: ans = None insert2.append(ans) self.logger.info( Insert command %s % insert ) self.cursor.execute(insert) The question is how do you tell that the data you were passed is a list or not? Thanks so much! -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
In article [EMAIL PROTECTED], rh0dium [EMAIL PROTECTED] wrote: The question is how do you tell that the data you were passed is a list or not? x = [] isinstance (x, list) True -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
rh0dium [EMAIL PROTECTED] writes: I want this function to be smart enough to tell if it's a list and do the funky concatonation otherwise don't. Bad code smell. Don't try to be too clever with the data types passed to you; instead, operate on them as though the caller has passed the right thing. Write unit tests and integration tests to ensure that the code is behaving as expected, and to reduce the amount of clever code that gets in the way of understanding the function. The question is how do you tell that the data you were passed is a list or not? With difficulty, since strings are sequences. It's debatable whether this is a wart. Two options: Use 'isinstance', which unfortunately breaks the rule of duck typing. Currently there's no good duck-typing way to differentiate strings from other sequences. if isinstance(x, basestring): # do string stuff else: # do sequence-of-string stuff Or: If you want to operate on sequences of strings, simply specify that's all that can be passed and expect it inside your function. This is more Pythonic, IMO. -- \ First they came for the verbs, and I said nothing, for verbing | `\weirds language. Then, they arrival for the nouns and I speech | _o__)nothing, for I no verbs. -- Peter Ellis | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
Ben Finney [EMAIL PROTECTED] wrote: Currently there's no good duck-typing way to differentiate strings from other sequences. I suppose you could do something like: try: foo.isalpha except AttributeError: print foo is not a string but other than proving that you don't *have* to use isinstance(), I don't think that approach has much going for it. -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
import types type() is types.ListType False type() is types.StringType True type([]) is types.StringType False type([]) is types.ListType True -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
Roy Smith [EMAIL PROTECTED] writes: Ben Finney [EMAIL PROTECTED] wrote: Currently there's no good duck-typing way to differentiate strings from other sequences. I suppose you could do something like: try: foo.isalpha except AttributeError: print foo is not a string but other than proving that you don't *have* to use isinstance(), I don't think that approach has much going for it. Duck typing preserves one very important feature of Python: a class doesn't have to *inherit from* type 'foo' to be a *substitute for* type 'foo'. An 'isinstance' check will fail on objects that don't inherit from the string types, but do implement the interface adequately. In this example, if an object 'x' implements the behaviour you're going to use, but doesn't inherit from 'basestring', refusing it just because 'isinstance(x, basestring)' is False would be the wrong choice. -- \ I planted some bird seed. A bird came up. Now I don't know | `\ what to feed it. -- Steven Wright | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: How to tell if function was passed a list or a string?
[EMAIL PROTECTED] writes: import types type() is types.ListType False type() is types.StringType True type([]) is types.StringType False type([]) is types.ListType True This is even worse than an 'isinstance' check; it refuses even subclasses of the types you accept, breaking polymorphism *and* inheritance. -- \ What you have become is the price you paid to get what you | `\ used to want. -- Mignon McLaughlin | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
