(Python) How to handle and work with each distinct lines in a string?

Question

I am trying to do exercise about "Filtering the file contents" and here is the full questions:

Create a program which reads all of the lines from the file and tests the lines. If the line has only letters and/or numbers, the program prints "[line] was ok.". If the line has special characters, the program should print "[line] was invalid.". When the program works, it prints out something like this:

>>> 
5345m345ö34l was ok.
no2no123non4 was ok.
noq234n5ioqw#% was invalid.
%#""SGMSGSER was invalid.
doghdp5234 was ok.
sg,dermoepm was invalid.
43453-frgsd was invalid.
hsth())) was invalid.
bmepm35wae was ok.
vmopaem2234+0+ was invalid.
gsdm12313 was ok.
bbrbwb55be3"?"#? was invalid.
"?"#%#"!%#"&"?%%"?#?#"?" was invalid.
retrte#%#?% was invalid.
abcdefghijklmnopqrstuvxy was ok.
>>>

It is advisable to read the lines one at a time, test them with the isalmun() string test and go on from there. Also remember that the strings may also end in a line break (\n), which is allowed, but fails the .isalnum() test if not sliced away.

Here is my implementation:

n=open("strings.txt","r")
x=n.read()
if x.isalnum()==True:
    print(x,"  was ok")
else:
    print(x," was invalid")
n.close()

And the system's response:

5345m34534l
no2no123non4
noq234n5ioqw#%
%#""SGMSGSER
doghdp5234
sg,dermoepm
43453-frgsd
hsth()))
bmepm35wae
vmopaem2234+0+
gsdm12313
gswrgsrdgrsgsig45
)/(/)(#=%#)%/
++-+-+--+--+-+>-<+-<<_<-+>>++.
  was invalid

I really don't know how to solve this. Please help me with what I have missed

Thank you in advance!!!

Have a think about implementing a `for` loop to iterate the lines (i.e. read each line in turn). — S3DEV, Sep 10 '20 at 06:47
[print(line+' was ok') if line.isalnum() else print(line+ ' was invalid') for line in open('file1.txt', 'r').read().splitlines()] — Deepak Tripathi, Sep 10 '20 at 07:02

score 1 · Accepted Answer · answered Sep 10 '20 at 06:55

1

something like this - the code needs to loop over the file line by line

with open('strings.txt') as f:
  lines = [l.strip() for l in f.readlines()]
  for line in lines:
    if line.isalnum():
      print(f'{line} was ok')
    else:
      print(f'{line} was invalid')

answered Sep 10 '20 at 06:55

balderman

22,927
7
34
52

HI, thank you it works. However, I have just started with Python so the first two lines are too complex for me to understand, can you explain it in a simplier way?? or it must be like that? – Danh Nguyễn Sep 10 '20 at 09:41
@DanhNguyễn see https://book.pythontips.com/en/latest/context_managers.html#context-managers for `with open()` and https://www.programiz.com/python-programming/list-comprehension for the second line. It does not have to be like this but it is the proper way to do it. Feel free to up vote. – balderman Sep 10 '20 at 09:50
@DanhNguyễn - Of the answers given, this is the Pythonic way to accomplish the task. This is the correct answer. Also, an excellent learning opportunity. – S3DEV Sep 10 '20 at 12:22
Thanks you very much for this useful knowledge! – Danh Nguyễn Sep 10 '20 at 14:57

score 0 · Answer 2 · answered Sep 10 '20 at 06:56

You may need to loop over your lines with a for loop. The way you're doing it now is, that all of your lines are stored under x. Something like this:

file = open("strings.txt","r")

for line in file:
  if line.isalnum()==True:
    print(line,"  was ok")
  else:
    print(line," was invalid")

file.close()

RomanR · Answer 3 · 2020-09-10T14:14:21.540

0

     n = open("strings.txt", "r", encoding="utf8")
for line in n:
    if line.strip().isalnum():
        print(line.strip(), " was ok")
    else:
        print(line.strip(), " was invalid")
n.close()

x = n.read() is a string consisting of all lines of the file . you need to read the file line by line with for.

strip() - Remove spaces at the beginning and at the end of the string,

edited Sep 10 '20 at 14:14

answered Sep 10 '20 at 07:00

RomanR

111
1
3

Hi with your implementation it goes with all "invalid". – Danh Nguyễn Sep 10 '20 at 09:58
Yes, I forgot to cat the end-of-line characters before comparing.I also added UTF8 encoding to the file read. Now the characters of the German alphabet are recognized as letters.(as in the first line for example) – RomanR Sep 10 '20 at 14:13

(Python) How to handle and work with each distinct lines in a string?

3 Answers3