Where to place the return statement when defining a function to read in a file using with open(...) as ...? - python-3.x

Question

I have a text file consisting of data that is separated by tab-delimited columns. There are many ways to read data in from the file into python, but I am specifically trying to use a method similar to one outlined below. When using a context manager like with open(...) as ..., I've seen that the general concept is to have all of the subsequent code indented within the with statement. Yet when defining a function, the return statement is usually placed at the same indentation as the first line of code within the function (excluding cases with awkward if-else loops). In this case, both approaches work. Is one method considered correct or generally preferred over the other?
def read_in(fpath, contents=[], row_limit=np.inf):
"""
fpath is filelocation + filename + '.txt'
contents is the initial data that the file data will be appeneded to
row_limit is the maximum number of rows to be read (in case one would like to not read in every row).
"""
nrows = 0
with open(fpath, 'r') as f:
for row in f:
if nrows < row_limit:
contents.append(row.split())
nrows += 1
else:
break
# return contents
return contents
Below is a snippet of the text-file I am using for this example.
1996 02 08 05 17 49 263 70 184 247 126 0 -6.0 1.6e+14 2.7e+28 249
1996 02 12 05 47 26 91 53 160 100 211 236 2.0 1.3e+15 1.6e+29 92
1996 02 17 02 06 31 279 73 317 257 378 532 9.9 3.3e+14 1.6e+29 274
1996 02 17 05 18 59 86 36 171 64 279 819 27.9 NaN NaN 88
1996 02 19 05 15 48 98 30 266 129 403 946 36.7 NaN NaN 94
1996 03 02 04 11 53 88 36 108 95 120 177 1.0 1.5e+14 8.7e+27 86
1996 03 03 04 12 30 99 26 186 141 232 215 2.3 1.6e+14 2.8e+28 99
And below is a sample call.
fpath = "/Users/.../sample_data.txt"
data_in = read_in(fpath)
for i in range(len(data_in)):
print(data_in[i])
(I realize that it's better to use chunks of pre-defined sizes to read in data, but the number of characters per row of data varies. So I'm instead trying to give user control over the number of rows read in; one could read in a subset of the rows at a time and append them into contents, continually passing them into read_in - possibly in a loop - if the file size is large enough. That said, I'd love to know if I'm wrong about this approach as well, though this isn't my main question.)

Answer 1

If your function needs to do some other things after writing to the file, you usually do it outside the with block. So essentially you need to return outside the with block too.
However if the purpose of your function is just to read in a file, you can return within the with block, or outside it. I believe none of the methods are preferred in this case.
I don't really understand your second question.

Answer 2

You can put return also withing with context.
By exiting context, the cleanup are done. This is the power of with, not to need to check all possible exit paths. Note: also with exception inside with the exit context is called.
But if file is empty (as an example), you should still return something. So in such case your code is clear, and follow the principle: one exit path. But if you should handle end of file without finding something important, I would putting normal return within with context, and handle the special case after it.