一种更好的方式来读取文本的子字符串而无需循环/ python

Question

I am reading lines from a file and then traversing each overlapping substring of k size in a loop, then process these strings. What would be a better (more efficient and elegant) way to read in the substrings? How can I make a list without the loop?

for line in lines[1::4]:
    startIdx = 0
    while startIdx + k <= len(line):
        substring = line[startIdx:(startIdx+k)]
        countFromSb[substring] = countFromSb.get(substring, 0) + 1
        startIdx += 1
    linesProcessed += 1

Answer 1

It can be made more elegant by using a collections.Counter instance

countFromSb = Counter()
# ...
n = -1
for n, line in enumerate(lines[1::4]):
    countFromSb.update(line[i:i+k] for i in range(1+len(line)-k))
lines_processed = n + 1

Answer 2

You can't iterate over the fixed-size slices of a sequence any faster than O(N), so your current approach is already as efficient as it gets.

In terms of elegance, you could abstract the iteration into its own function, which will keep your current scope less cluttered with one letter variable names:

def iter_slices(s, size):
    for i in range(len(s)-size+1):
        yield s[i:i+size]

for line in lines[1::4]:
    for substring in iter_slices(line, k):
        countFromSb[substring] = countFromSb.get(substring, 0) + 1
    linesProcessed += 1

This can also be combined with Gribouillis' suggestion to use a Counter, eliminating the for blocks entirely:

countFromSb = Counter(substring for line in lines[1::4] for substring in iter_slices(line, k))