Both work differently. The list comprehension version takes advantage of the special bytecode LIST_APPEND which calls PyList_Append directly for us. Hence it avoids an attribute lookup to list.append and a function call at the Python level. >>> def func_lc(): [x**2 for x in y] … >>> dis.dis(func_lc) 2 0 LOAD_CONST 1 (<code object <listcomp> at … Read more
It is legal, and the general rule is that you do need parentheses around a generator expression. As a special exception, the parentheses from a function call also count (for functions with only a single parameter). (Documentation) Note that testing if my_string appears in my_list is as easy as my_string in my_list No generator expression … Read more
Because the syntax of takewhile() and dropwhile() is not the clearest, here are the actual examples of your question: >>> [i for i in itertools.takewhile(lambda x: x*x<30, range(10))] [0, 1, 2, 3, 4, 5] >>> [i for i in itertools.dropwhile(lambda x: x*x<30, range(10))] [6, 7, 8, 9] Know that the author of itertools has questioned … Read more
They are different, because the value of i in both the generator expression and the list comp are evaluated lazily, i.e. when the anonymous functions are invoked in f. By that time, i is bound to the last value if t, which is -1. So basically, this is what the list comprehension does (likewise for … Read more
If you use any(lst) you see that lst is the iterable, which is a list of some items. If it contained [0, False, ”, 0.0, [], {}, None] (which all have boolean values of False) then any(lst) would be False. If lst also contained any of the following [-1, True, “X”, 0.00001] (all of which … Read more
Note: this was a bug in the CPython’s handling of yield in comprehensions and generator expressions, fixed in Python 3.8, with a deprecation warning in Python 3.7. See the Python bug report and the What’s New entries for Python 3.7 and Python 3.8. Generator expressions, and set and dict comprehensions are compiled to (generator) function … Read more
Expanding on Paulo‘s answer, generator expressions are often slower than list comprehensions because of the overhead of function calls. In this case, the short-circuiting behavior of in offsets that slowness if the item is found fairly early, but otherwise, the pattern holds. I ran a simple script through the profiler for a more detailed analysis. … Read more