How to simplify my working Python3 regex and make it more Pythonic

Question

I created a working (long) bit of code to check if a file exists in a directory or not and if so to extract two string values and convert them to float.

try:
    # use the file name from earlier and append .HDR
    filename = sel_file +'.HDR'

    # open the text file if found, read in the file
    f = open(filename, 'r+')
    data = f.read()
    f.close()

    # these regex are to look for the 2 strings and extracts the values in quotation marks after them
    # the value in quotes is a number written as string. There is only 1 CTRW & several PTR
    c_pat = r'CTRW,\"(.*?)\"'
    p_pat = r'\nPTR,\"(.*?)\"'

    # implements the regex on the file
    c = re.findall(c_pat, data)
    p = re.findall(p_pat, data)

    # for some reason the c & p are saved as lists so this converts to a string and then a float
    ctrw_str = int(float( ''.join(map(str,c))))
    ptr_str = int(float(''.join(map(str,p))))

    # saves to the necessary variable for use later in the code
    CTRW = ctrw_str
    PTR = ptr_str

except IOError:
    # If the file is not in the directory then the following values are used
    CTRW = 120
    PTR = 197
    pass

The file is read in as a string but for some unknow reason the regex captures and creates a list, which is not a huge deal but requires the extra step of converting to a string and then a float.

The search for the PTR value returns several within the source file but the the one I want is exactly PTR which is why I used the \n for the p_pat regex search and not in the c_pat regex.

I would like to see if any here have a good idea of how to shrink this into less lines and make it more Pythonic.

Can you clarify, does the file have multiple instances of PTR,"123" ? — Marcel Wilson
– Marcel Wilson, Commented Nov 9, 2020 at 21:47
Yes, it is written in the comments: "There is only 1 CTRW & several PTR", but you also mention you need "to extract two string values and convert them to float". Which is true? — Ryszard Czech
– Ryszard Czech, Commented Nov 9, 2020 at 22:03
a sample within the larger file that I am looking at has a single instance of CTRW,"200" and a single instance of exactly PTR,"175.00" but there are are versions of the string PTR located with other characters. within one text file there are ~11 instances of the string PTR, including PTR, PTRXA, PTRXB, DNPTR1, and TWCPTR. I am trying to grab the numbers in quotes so I can use them later within calculations with voltage and current values located in a seperate COMTRADE file. — Neil S
– Neil S, Commented Nov 9, 2020 at 22:52

Ryszard Czech · Accepted Answer · 2020-11-09 22:08:00Z

1

No wonder you get lists, re.findall returns a list of found strings.

If - as you say - you want "to extract two string values and convert them to float" use re.search to fetch the first match:

try:
    filename = sel_file +'.HDR'
    with open(filename, 'r+') as f:
        data = f.read()
        c = re.search(r'CTRW,"([^"]*)"', data)
        if c:
            CTRW = int(float(c.group(1)))
        p = re.search(r'\nPTR,"([^"]*)"', data)
        if p:
            PTR = int(float(p.group(1)))
except IOError: # If the file is not in the directory then the following values are used
    CTRW = 120
    PTR = 197
    pass

answered Nov 9, 2020 at 22:08

Ryszard Czech

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2 Comments

Neil S Over a year ago

The above worked and definitely looks better than my hacked together version. Appreciate it.

Ryszard Czech Over a year ago

@Neil Please kindly upvote the answer if it is helpful.

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