Python RE to search digit along with decimal

Question

I am trying to pull the digit values (100.00 & 200.00) using pythons regular expressions , but when I invoke the code it doesn't yield anything... I am using python version 2.7

1) My file name is "file100" from where I need to opt the values..

# cat file100
Hi this doller 100.00
Hi this is doller 200.00

2) This is my python code..

# cat count100.py
#!/usr/bin/python
import re
file = open('file100', 'r')
for digit in file.readlines():
        myre=re.match('\s\d*\.\d{2}', digit)
        if myre:
           print myre.group(1)

3) While I am running this code , it does not yield anything , no error .. nothing ..

# python   count100.py

Answer 1

Use re.search instead:

import re
file = open('file.txt', 'r')
for digit in file.readlines():
    myre = re.search(r'\s\b(\d*\.\d{2})\b', digit)
    if myre:
        print myre.group(1)

Results

100.00
200.00

From the documentation:

Scan through string looking for the first location where the regular expression pattern produces a match

If you decided to use a group, parentheses are also needed:

(...) Matches whatever regular expression is inside the parentheses, and indicates the start and end of a group; the contents of a group can be retrieved after a match has been performed, and can be matched later in the string with the \number special sequence, described below. To match the literals '(' or ')', use ( or ), or enclose them inside a character class: [(] [)].

re.match is only valid:

If zero or more characters at the beginning of string match the regular expression pattern

r to enclose regex as raw strings:

String literals may optionally be prefixed with a letter 'r' or 'R'; such strings are called raw strings and use different rules for interpreting backslash escape sequences.

...

Unless an 'r' or 'R' prefix is present, escape sequences in strings are interpreted according to rules similar to those used by Standard C

Answer 2

If they are always at the end of your lines just rsplit once and pull the last element:

with open('file100', 'r') as f:
    for line in f:
        print(line.rsplit(None, 1)[1])

Output:

100.00
200.00

rsplit(None,1) just means we split once from the end of the string on whitespace, then we pull the second element:

In [1]: s = "Hi this doller 100.00"

In [2]: s.rsplit(None,1)
Out[2]: ['Hi this doller', '100.00']

In [3]: s.rsplit(None,1)[1]
Out[3]: '100.00'

In [4]: s.rsplit(None,1)[0]
Out[4]: 'Hi this doller'

If you really need a regex use search:

import re

with open('file100', 'r') as f:
    for line in f:
        m = re.search(r"\b\d+\.\d{2}\b",line)
        if m:
            print(m.group())

Answer 3

Your primary problem is that you're using re.match which requires a match starting from the beginning of the string, not re.search, which allows a match that can start at any point in the string. I'll break down my recommendations, though:

import re

No need to recompile on every loop (Python actually caches some regexes for you, but keep one in a reference to be safe). I'm using a VERBOSE flag to break apart the regex for you. Use a r to precede your string so that backslashes aren't escaping the characters they precede as Python reads the string:

regex = re.compile(r'''
  \s      # one whitespace character, though I think this is perhaps unnecessary
  \d*     # 0 or more digits
  \.      # a dot
  \d{2}   # 2 digits
  ''', re.VERBOSE) 

Use a context manager and open the file with universal newlines, 'rU' mode, so that no matter what platform the file was created on, you will be able to read it line by line.

with open('file100', 'rU') as file:

Don't use readlines, which loads the entire file into memory at once. Instead, use the file object as an iterator:

    for line in file:
        myre = regex.search(line) 
        if myre:
            print(myre.group(0)) # access the first group, there are no  
                                 # capture groups in your regex

My code prints:

100.00
200.00

Answer 4

There's a couple problems here:

1. .match only looks for matches at the beginning of a string -- see search() vs. match().

2. You're not using capture groups, so there's no reason why .group(1) of myre.group(1) would have any content

Here's an updated sample:

import re

file = """
Hi this doller 100.00
Hi this is doller 200.00
"""

for digit in file.splitlines():
    myre = re.search('\s\d*\.\d{2}', digit)
    if myre:
        print(myre.group(0))