Python list comprehension and list.remove()

Question

The list signals_by_date stores tuples and each tuple contains 15 numbers. For each tuple within signals_by_date, I want to remove numbers that don't satisfy certain criteria. For some reason, no matter what constraints I put in the list comprehension, I'm always left with 7 numbers in each tuple. In the code example below, all numbers are less than 3, so I would expect each tuple to be empty. What am I doing wrong? Many thanks.

    signals_by_date = []
    for i in range(0, 1):
        temp_signals = []
        for symbol in symbols:        
            for signal in signals_by_symbol[symbol]:
            temp_signals.append(signal[i]-1)
        signals_by_date.append(temp_signals)
        [signals_by_date[i].remove(v) for v in signals_by_date[i] if v < 3]

Answer 1

最后一行应为：

signals_by_date[i] = [v for v in signals_by_date[i] if v >= 3]

Answer 2

Presumably, as you remove each item you're shifting the items in the list such that you skip seeing every second one.

In general, I believe list comprehensions are intended to accrue new lists from existing ones rather than to produce side effects on the items in the original list; and certainly not to change the structure of the comprehended list.