Python list comprehensions nasty behavior
Python’s list comprehension syntax is amazingly concise and easy to use and understand. It make Python even more beautiful than it already is.
However, i came upon some weird behavior today that caused a strange bug in my application.
The common way to use a list comprehension is with a variable named x eg:
my_new_list = [ x.name for x in people ]
The behavior most of us would expect (or assume to be reasonable) is for the scope of variable x to be limited within the execution of the list comprehension.
This is not the case however. If you already have defined an x variable and expect it to be the same after the list comprehension you will be disappointed (not to mention bewildered at your new, seemingly unexplained, bug ).
I am not sure why this feature it was designed that way. I think this is a source of confusion and, as such, un-pythonic, if i may use the term :-)
Be careful when using list comprehensions to use a completely new variable.