Read text line by line in python

Question

I would like to make a script that read a text line by line and based on lines if it finds a certain parameter populates an array. The idea is this

Read line
if Condition 1
  #True
  nested if Condition 2
...
else Condition 1 is not true
  read next line

I can't get it to work though. I'm using readline () to read the text line by line, but the main problem is that the command never works to make it read the next line. Can you help me? Below an extract of my actual code:

col = 13     # colonne
rig = 300    # righe

a = [ [ None for x in range(col) ] for y in range(rig) ] 

counter = 1
file = open('temp.txt', 'r')
files = file.readline()
for line in files:
 if 'bandEUTRA: 32' in line:
  if 'ca-BandwidthClassDL-EUTRA: a' in line:
   a[counter][5] = 'DLa'
   counter = counter + 1
  else:
   next(files)
 else:
  next(files) 

print('\n'.join(map(str, a)))

Answer 1

Fixes for the code you asked about inline, and some other associated cleanup, with comments:

col = 13     # colonne
rig = 300    # righe

a = [[None] * col for y in range(rig)]  # Innermost repeated list of immutable
                                        # can use multiplication, just don't do it for
                                        # outer list(s), see: https://stackoverflow.com/q/240178/364696

counter = 1
with open('temp.txt') as file:  # Use with statement to get guaranteed file closure; 'r' is implicit mode and can be omitted
    # Removed: files = file.readline()  # This makes no sense; files would be a single line from the file, but your original code treats it as the lines of the file
    # Replaced: for line in files:  # Since files was a single str, this iterated characters of the file

    for line in file:  # File objects are iterators of their own lines, so you can get the lines one by one this way
        if 'bandEUTRA: 32' in line and 'ca-BandwidthClassDL-EUTRA: a' in line:  # Perform both tests in single if to minimize arrow pattern
            a[counter][5] = 'DLa'
            counter += 1  # May as well not say "counter" twice and use +=

    # All next() code removed; next() advances an iterator and returns the next value,
    # but files was not an iterator, so it was nonsensical, and the new code uses a for loop that advances it for you, so it was unnecessary.

    # If the goal is to intentionally skip the next line under some conditions, you *could*
    # use next(files, None) to advance the iterator so the for loop will skip it, but
    # it's rare that a line *failing* a test means you don't want to look at the next line
    # so you probably don't want it

# This works:
print('\n'.join(map(str, a)))
# But it's even simpler to spell it as:
print(*a, sep="\n")
# which lets print do the work of stringifying and inserting the separator, avoiding 
# the need to make a potentially huge string in memory; it *might* still do so (no documented
# guarantees), but if you want to avoid that possibility, you could do:
sys.stdout.writelines(map('{}\n'.format, a))
# which technically doesn't guarantee it, but definitely actually operates lazily, or
for x in a:
    print(x)
# which is 100% guaranteed not to make any huge strings

Answer 2

You can do:

with open("filename.txt", "r") as f:
    for line in f:
        clean_line = line.rstrip('\r\n')
        process_line(clean_line) 

Edit: for your application of populating an array, you could do something like this:

with open("filename.txt", "r") as f:
    contains = ["text" in l for l in f]

This will give you a list of length number of lines in filename.txt, the contents of the array will be False for each line that doesn't contain text, and True for each line that does.

Edit 2: To reflect @ShadowRanger's comments, I've changed my code to not do iterate over each line in the file without reading the whole thing at once.