Question

I’m trying to change some elements of a list based on the properties of previous ones. Because I need to assign an intermediate variable, I don’t think this can be done as a list comprehension. The following code, with comment, is what I’m trying to achieve:

for H in header:
    if "lower" in H.lower():
        pref="lower"
    elif "higher" in H.lower():
        pref="higher"
    if header.count(H) > 1:
        # change H inplace
        H = pref+H

The best solution I’ve come up with is:

for ii,H in enumerate(header):
    if "lower" in H.lower():
        pref="lower"
    elif "higher" in H.lower():
        pref="higher"
    if header.count(H) > 1:
        header[ii] = pref+H

It doesn’t quite work, and feels un-pythonic to me because of the indexing. Is there a better way to do this?

Concrete example:

header = ['LowerLevel','Term','J','UpperLevel','Term','J']

desired output:

header = ['LowerLevel','LowerTerm','LowerJ','UpperLevel','UpperTerm','UpperJ']

Note that neither of my solutions work: the former never modifies header at all, the latter only returns
header = ['LowerLevel','LowerTerm','LowerJ','UpperLevel','Term','J']
because count is wrong after the modifications.

Answer 1

header   = ['LowerLevel','Term','J','UpperLevel','Term','J']
prefixes = ['lower', 'upper']

def prefixed(header):
    prefix = ''

    for h in header:
        for p in prefixes:
            if h.lower().startswith(p):
                prefix, h = h[:len(p)], h[len(p):]
        yield prefix + h

print list(prefixed(header))

I don’t really know that this is better than what you had. It’s different…

$ ./lower.py
['LowerLevel', 'LowerTerm', 'LowerJ', 'UpperLevel', 'UpperTerm', 'UpperJ']