Regex: Perl to Python

[Peter Otten]

Fillmore wrote:

> 
> Hi, I'm trying to move away from Perl and go to Python.
> Regex seems to bethe hardest challenge so far.
> 
> Perl:
> 
> while (<HEADERFILE>) {
>      if (/(\d+)\t(.+)$/) {
> print $1." - ". $2."\n";
>      }
> }
> 
> into python
> 
> pattern = re.compile(r"(\d+)\t(.+)$")
> with open(fields_Indexfile,mode="rt",encoding='utf-8') as headerfile:
>      for line in headerfile:
>          #sys.stdout.write(line)
>          m = pattern.match(line)
>          print(m.group(0))
>      headerfile.close()
> 
> but I must be getting something fundamentally wrong because:
> 
> Traceback (most recent call last):
>    File "./slicer.py", line 30, in <module>
>      print(m.group(0))
> AttributeError: 'NoneType' object has no attribute 'group'
> 
> 
>   why is 'm' a None?

match() matches from the begin of the string, use search():

match = pattern.search(line)
if match is not None:
    print(match.group(1), "-", match.group(2))

Also, in Python you often can use string methods instead of regular 
expressions:

index, tab, value = line.strip().partition("\t")
if tab and index.isdigit():
    print(index, "-", value)

> the input data has this format:
> 
>           :
>       3	prop1
>       4	prop2
>       5	prop3
>