I am wondering if Python has the concept of storing data in the default variable in for loop.
For example, in perl, the equivalent is as follow
foreach (@some_array) {
print $_
}
Thanks, Derek
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2There is not, and there should not be. "Explicit is better than implicit". For other pratices, stick with other languages. This is one of the worst part of Perl.jsbueno– jsbueno2010-11-22 17:17:03 +00:00Commented Nov 22, 2010 at 17:17
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4 Answers
No. You should just use
for each in some_array:
print each
Comments
Just for fun, here's something that does just about what you desire. By default it binds the loop variable to the name "_each", but you can override this with one of your own choosing by supplying a var keyword argument to it.
import inspect
class foreach(object):
__OBJ_NAME = '_foreach'
__DEF_VAR = '_each'
def __init__(self, iterable, var=__DEF_VAR):
self.var = var
f_locals = inspect.currentframe().f_back.f_locals
if self.var not in f_locals: # inital call
self.iterable = iter(iterable)
f_locals[self.__OBJ_NAME] = self
f_locals[self.var] = self.iterable
else:
obj = f_locals[self.__OBJ_NAME]
self.iterable = obj.each = obj.iterable
def __nonzero__(self):
f_locals = inspect.currentframe().f_back.f_locals
try:
f_locals[self.var] = self.iterable.next()
return True
except StopIteration:
# finished - clean up
del f_locals[self.var]
del f_locals[self.__OBJ_NAME]
return False
some_array = [10,2,4]
while foreach(some_array):
print _each
print
while foreach("You can do (almost) anything in Python".split(), var='word'):
print word
2 Comments
aaronasterling
Unfortunately, like all of these hacks using
f_locals, it only works in the global scope. If you want to use it deeper in a function, you have to use one more f_back for each additional level. Eventually you figure out that you're actually just using globals(). +1 though. Good trick.
martineau
@aaronasterling: I know, since I more-or-less got the idea from your answer to switch case in python doesn't work; need another pattern -- and our prolonged discussion of it. ;-) Those facts are also why I began my answer here with "Just for fun".
Python allows the use of the '_' variable (quotes mine). Using it in a program seems to be the Pythonic way to have a loop control variable that is ignored in the loop (see other questions, e.g. Is it possible to implement a Python for range loop without an iterator variable? or my Pythonic way to ignore for loop control variable). As a comment pointed out, this isn't the same as Perl's default variable, but it allows you to do something like:
some_list = [1, 2, 3]
for _ in some_list:
print _
A guru may correct me, but I think this is about as close as you'll get to what you're looking for.
5 Comments
Ignacio Vazquez-Abrams
No, there is no such default variable.
_ is just another valid name.
GreenMatt
@Ignacio Vazquez-Abrams: Yeah, you're right, but to me it seems analogous. Answer edited.
unholysampler
_ only exists in the python shell. bytes.com/topic/python/answers/… The example you give is no different than using a normal variable name.GreenMatt
@unholysampler: I don't recall using _ in the Python shell before, thanks for pointing that out. FWIW, _ does allow you to avoid pylint warnings about variable names being too short or not used (see the link in my answer to my earlier question).
Whatever is used in the for loop syntax becomes the variable that that item in the iteration is stored against for the remainder of the loop.
for item in things:
print item
or
for googleplexme in items:
print googleplexme
The syntax looks like this
for <given variable> in <iterable>:
meaning that where given variable can be anything you like in your naming space and iterable can be an iterable source.
