python - Iterate over list of strings to pull out substrings

Question

I have a long list of different strings that all contain some information about a specific port across the globe. However, each port name is different and is contained in a different location within the string. What I want to do is loop over all of the strings, find the word 'Port' and then store the next two substrings after 'Port'. For example:

'Strong winds may disrupt operations at the Port of Rotterdam on July 5'

I find 'Port' and now want 'of Rotterdam' to be added onto 'Port' as a complete string, like 'Port of Rotterdam'. I thought there could be some way to split up each longer string by doing parts = my_str.split(' '). Then:

for i in parts:
    if i == 'Port':
        new_str = i

However, I am not sure how to add on the next two substrings. Ideas?

Answer 1

Take a look at list.index (also documented here):

parts = my_str.split(' ')
try:
    port_index = parts.index('Port')
except ValueError:
    pass # Port name not found
else:
    port_name = ' '.join(parts[port_index:port_index + 2])

You can of course do more advanced processing. For example, grab a sequence of uppercased words optionally preceded by a single of:

def find_name(sentence):
    """
    Get the port name or None.
    """
    parts = sentence.split(' ')
    try:
        start = parts.index('Port')
    except ValueError:
        return None
    else:
        if start == len(parts) - 1:
            return None

    end = start + 1
    if parts[end] == 'of':
        end = end + 1
    while end < len(parts) and parts[end][0].isupper():
        end += 1

    if end == start + 1 or (end == start + 2 and parts[start + 1] == 'of'):
        return None

    return ' '.join(parts[start:end])

Of course you can do the same thing with regex:

pattern = re.compile(r'Port(?:s+of)?(s+[A-Z]S+)+')
match = pattern.search(my_str)
print(match.group())

This regex will not properly match non-latin uppercase letters. You may want to investigate the solutions here for sufficiently foreign port names.

Both of the solutions here will work correctly for the following two test cases:

'Strong winds may disrupt operations at the Port of Rotterdam on July 5'
'Strong winds may disrupt operations at the Port of Fos-sur-Mer on July 5'
'Strong winds may disrupt operations at Port Said on July 5'

You can likely improve the search further, but this should give you the tools to get a solid start. At some point, if the sentences become complex enough, you may want to use natural language processing of some kind. For example, look into the nltk package.