I currently have
seq1 = "--MFA"
seq2= "--MFU"
for i in range(0, len(seq1)):
if seq1[i] or seq2[i] == '-':
print "hi"
else:
print "bye"
Why does it print "hi" 5 times (even if seq1[i] and seq1[i] are M, F, A/U). I thought it was a regex problem at first, but even escaping the hyphen yielded the same results.
if seq1[i] or seq2[i] == '-':
Means:
if (seq1[i]) or (seq2[i] == '-'):
If seq[i] has a value of True (i.e, if bool(seq1[i]) == True), then the conditional statement will instantly be true, because of the or. With an or operator, if one side is True, then the conditional runs.
Note that bool(seq1[i]) will always be True because a string with any length is considered True.
Hence, 'hi' is printed.
if seq1[i] or seq2[i] == '-':
This condition means that if seq1[i] is true or seq2[i] = '-' do the following. In that case, seq1[i] is true the 5 times. Then, it prints 'hi' 5 times.
There are a number of alternatives you could use here
if '-' in (seq1[i], seq2[i]):
Is concise, but is funny to read.
if seq1[i] == '-' or seq2[i] == '-':
Feels more natural
A cleaner way to loop through the sequences together is to use zip
for i, j in zip(seq1, seq2):
if i == '-' or j == '-':
print "hi"
else:
print "bye"
If you were looping through more sequences together, a good way to extend the comparison is to use any
for item in zip(seq1, seq2, seq3, seq4, ...):
if any(i == '-' for i in item):
print "hi"
else:
print "bye"
'-' or '2' >>> '-''-' or '2' == '-' >>> '-'So you can guess that it always return the left part because it's interpreted as True.