What does Python mean? The syntax is a bit strange?

Question

filelist = [x for x in os.listdir() if os.path.isfile(x)]

Answer 1

Equivalent to:

filelist = []
for x in os.listdir():
    if os.path.isfile(x):
        filelist.append(x)
    

This is the content of list parsing.

Answer 2

List generation
is equivalent to. os.listdir() requires a parameter, which path you want to get the list.

In [54]: filelist = []

In [55]: for x in os.listdir("."):
    ...:     if os.path.isfile(x):
    ...:         filelist.append(x)
    ...:

In [56]:

Using list generation is a little faster than [].append(). You can test it using large batches. Why fast. The mechanism of the python listobject model is related. If you have time, you can read the python source code, which is written in C language

Answer 3

Definition:
List comprehensions (also known as list comprehensions) provide a concise and concise way to create lists.

Specification:
variable = [out_exp for out_exp in input_list if out_exp == 2]

Example:
multiples = [i for i in range(30) if i % 3 is 0]
print(multiples)

Output: [0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

Scenario:
When the logic in the loop is relatively simple, it can be replaced by derivation to increase code readability and cleanliness

Answer 4

List comprehensions
List generation

The order is as follows: