I'd like to know the best way (more compact and "pythonic" way) to do a special treatment for the last element in a for loop. There is a piece of code that should be called only between elements, being suppressed in the last one.
Here is how I currently do it:
for i, data in enumerate(data_list):
if i != len(data_list) - 1:
Most of the times it is easier (and cheaper) to make the first iteration the special case instead of the last one:
first = True for data in data_list: if first: first = False else: between_items() item()
This will work for any iterable, even for those that have no
file = open('/path/to/file') for line in file: process_line(line) # No way of telling if this is the last line!
Apart from that, I don't think there is a generally superior solution as it depends on what you are trying to do. For example, if you are building a string from a list, it's naturally better to use
str.join() than using a
for loop “with special case”.
Using the same principle but more compact:
for i, line in enumerate(data_list): if i > 0: between_items() item()
Looks familiar, doesn't it? :)
For @ofko, and others who really need to find out if the current value of an iterable without
len() is the last one, you will need to look ahead:
def lookahead(iterable): """Pass through all values from the given iterable, augmented by the information if there are more values to come after the current one (True), or if it is the last value (False). """ # Get an iterator and pull the first value. it = iter(iterable) last = next(it) # Run the iterator to exhaustion (starting from the second value). for val in it: # Report the *previous* value (more to come). yield last, True last = val # Report the last value. yield last, False
Then you can use it like this:
>>> for i, has_more in lookahead(range(3)): ... print(i, has_more) 0 True 1 True 2 False