def column(line, column = 0, tab_length = tab_length):
"""
returns the |column| offset that the cursor would end on if this
|line| were printed out on a perfect terminal, starting at |column|,
assuming tab stops at equal intervals of |tab_length|, where
|tab_length| is a power of two.
A perfect terminal is one which has no horizontal nor vertical size
constraints.
"""
# todo: consider: assumes that '\n' returns to column 0. It could
# possibly be more useful for it to return to the initial column
# offset. See comments in requirement assertions.
# note: not all white space of unicode are represented here, if it
# is ever generalized.
for character in line:
if character == '\t':
column = next_tab(column, tab_length)
elif character == '\r':
pass
elif character == '\n':
column = 0
else:
column += 1
return column
pass
elif character == '\n':
column = 0
else:
column += 1
return column
# unit tests
if __name__ == '__main__':
# for varying starting columns
for start in range(0, 4):
# core axiom
assert column("\t", start) == next_tab(start)
for count in range(0, 4):
# a count of spaces
assert column(" " * count, start) == start + count
# axiom applied to a count of spaces followed by a tab
example = " " * count + "\t"
assert column(example, start) == next_tab(start + count)
# up to three spaces before an indent
for n in range(0, 3):
assert column(" " * count + "\t") == 4
# a tab on the first tab stop