Argthtjtr

I generally like to use the with open(...) as file: idiom for opening files because it avoids failing to close a file, improves code readability, and improves exception handling. However, I have seen other people's code use one-liners to open and read/write a file without saving the TextIOWrapper object:

# Read a file

contents = open('the_file.txt').read()



# Write to a file

open('the_file.txt', 'w').write('This is the thing.')



# Write an empty file

open('empty_file.txt', 'w')

These idioms are appealing because of their simplicity, but I want to understand what python does with those file objects.

I tried using the dis module to inspect the bytecode, but I'm not sure how to read the output:

def myfunc():

    open('test.txt', 'w')

dis.dis(myfunc)

  2           0 LOAD_GLOBAL              0 (open)

              2 LOAD_CONST               1 ('test.txt')

              4 LOAD_CONST               2 ('w')

              6 CALL_FUNCTION            2

              8 POP_TOP

             10 LOAD_CONST               0 (None)

             12 RETURN_VALUE

def withfunc():

    with open('test.txt', 'w') as f:

        pass

dis.dis(withfunc)

  2           0 LOAD_GLOBAL              0 (open)

              2 LOAD_CONST               1 ('test.txt')

              4 LOAD_CONST               2 ('w')

              6 CALL_FUNCTION            2

              8 SETUP_WITH               6 (to 16)

             10 STORE_FAST               0 (f)



  3          12 POP_BLOCK

             14 LOAD_CONST               0 (None)

        >>   16 WITH_CLEANUP_START

             18 WITH_CLEANUP_FINISH

             20 END_FINALLY

             22 LOAD_CONST               0 (None)

             24 RETURN_VALUE

def savefunc():

    f = open('test.txt', 'w')

    f.close()

dis.dis(savefunc)

  2           0 LOAD_GLOBAL              0 (open)

              2 LOAD_CONST               1 ('test.txt')

              4 LOAD_CONST               2 ('w')

              6 CALL_FUNCTION            2

              8 STORE_FAST               0 (f)



  3          10 LOAD_FAST                0 (f)

             12 LOAD_ATTR                1 (close)

             14 CALL_FUNCTION            0

             16 POP_TOP

             18 LOAD_CONST               0 (None)

             20 RETURN_VALUE

I have two questions:

1. What happens under the hood when you use open without saving the TextIOWrapper object (especially regarding whether they are properly closed)


2. Are there reasons to NOT use the one-liners?