Question

It’s pretty hard to explain but here’s my issue..

sampleList = ['_ This is an item.','__ This is also an item']

I’m trying to take sampleList and find if _ occurs ONLY in the first character line, replace it with #, and then if __ occurs, replace with &.

It’s a bit hard to understand even for myself.

Basically if I have a list, I want it to work through the list, only find the FIRST instance of a possible dict and replace it with the corresponding value. And then return that entire list..

EDIT:

Sorry if I wasn’t descriptive enough..

dictarray = {
'_':'&',
'__':'*#',
'____':'*$(@'
}

sampleList = ['_ This is an item.','__ This is also an item','_ just another _ item','____ and this last one']

output:

sampleList = ['& This is an item.','*# This is also an item','& just another _ item','*$(@ and this last one']

I need to be able to capture if the key is found at the beginning of the item, if so, change it out for the value.

Answer 1

# The original input data
dictarray = {
'_':'&',
'__':'*#',
'____':'*$(@'
}

sampleList = ['_ This is an item.','__ This is also an item','_ just another _ item','____ and this last one']

# Order the substitutions so the longest are first.
subs = sorted(dictarray.items(), key=lambda pair: len(pair[0]), reverse=True)

def replace_first(s, subs):
    """Replace the prefix of `s` that first appears in `subs`."""
    for old, new in subs:
        if s.startswith(old):
            # replace takes a count of the number of replacements to do.
            return s.replace(old, new, 1)
    return s

# make a new list by replace_first'ing all the strings.
new_list = [replace_first(s, subs) for s in sampleList]

print new_list

produces:

['& This is an item.', '*# This is also an item', '& just another _ item', '*$(@ and this last one']

Here I’ve massaged the dictarray to order the substitution longest first, so that shorter prefixes don’t preclude longer ones.