Joining a list of non-string python objects that implement __str__ method, using the .join function [duplicate]
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I've already looked at this question on 开发者_如何转开发representing strings in Python but my question is slightly different. It is also different than the question How to concatenate (join) items in a list to a single string which was created after this question and applies to a list of strings and thus does not have any applicability to this question whatsoever (where the thrust of this question is specifically dealing with the challenge of non-string items).
Here's the code:
>>> class WeirdThing(object):
... def __init__(self):
... self.me = time.time()
... def __str__(self):
... return "%s" % self.me
... def __repr__(self):
... return ";%s;" % self.me
...
>>> weird_list = [WeirdThing(), WeirdThing(), WeirdThing()]
>>> print weird_list
[;1302217717.89;, ;1302217717.89;, ;1302217717.89;]
>>> "\n".join(weird_list)
Traceback (most recent call last):
File "<console>", line 1, in <module>
TypeError: sequence item 0: expected string, WeirdThing found
I realize that this works:
>>> "\n".join(str(wi) for wi in weird_list)
'1302217717.89\n1302217717.89\n1302217717.89'
>>>
Still it would be nice to avoid doing that every time I want to join the objects together. Is it simply not possible?
You have to stringify your objects before you can join them. This is because str.join
expects a series of strings, and you must give it a series of strings.
For the sake of less typing at the cost of readability, you can do "\n".join(map(str, list_of_things)
.
There are probably no amazing way.
def strjoin(glue, iterable):
return glue.join(str(s) for s in iterable)
"...it would be nice to avoid doing that every time..."
You want to avoid repeating that same code multiple times? Then use a function;:
def join_as_str(alist):
return "\n".join(str(item) for item in alist)
Would it work for you if you added an __add__
method? E.g.,
from operator import add
from random import randint
class WeirdThing(object):
def __init__(self,me=None):
self.me = me if me else chr(randint(97,122))
def __str__(self):
return "%s" % self.me
def __repr__(self):
return ";%s;" % self.me
def __add__(self,other):
new_me = add(str(self.me),str(other.me))
return WeirdThing(new_me)
weird_list = [WeirdThing(), WeirdThing(), WeirdThing()]
print weird_list
gives,
[;y;, ;v;, ;u;]
and this,
strange_thing = reduce(add,weird_list)
print strange_thing
gives,
yvu
You technically aren't joining the list of python objects, just their string representation.
>>> reduce(lambda x,y: "%s\n%s" % (x,y), weird_list)
'1302226564.83\n1302226564.83\n1302226564.83'
>>>
This works as well but doesn't look any nicer:
>>> a = ""
>>> for x in weird_list:
... a+="%s\n" % x
...
>>> print a
1302226564.83
1302226564.83
1302226564.83
>>>
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