def column_index_from_string(column, fast=False):
"""Convert a column letter into a column number (e.g. B -> 2)
Excel only supports 1-3 letter column names from A -> ZZZ, so we
restrict our column names to 1-3 characters, each in the range A-Z.
.. note::
Fast mode is faster but does not check that all letters
are capitals between A and Z
"""
column = column.upper()
clen = len(column)
if not fast and not all('A' <= char <= 'Z' for char in column):
msg = 'Column string must contain only characters A-Z: got %s' % column
raise ColumnStringIndexException(msg)
if clen == 1:
return ord(column[0]) - 64
elif clen == 2:
return ((1 + (ord(column[0]) - 65)) * 26) + (ord(column[1]) - 64)
elif clen == 3:
return ((1 + (ord(column[0]) - 65)) * 676) + (
(1 + (ord(column[1]) - 65)) * 26) + (ord(column[2]) - 64)
elif clen > 3:
raise ColumnStringIndexException(
'Column string index can not be longer than 3 characters')
else:
raise ColumnStringIndexException(
'Column string index can not be empty')
def get_column_letter(col_idx):
"""Convert a column number into a column letter (3 -> 'C')
Right shift the column col_idx by 26 to find column letters in reverse
order. These numbers are 1-based, and can be converted to ASCII
ordinals by adding 64.
"""
# these indicies corrospond to A -> ZZZ and include all allowed
# columns
if not 1 <= col_idx <= 18278:
msg = 'Column index out of bounds: %s' % col_idx
raise ColumnStringIndexException(msg)
ordinals = []
temp = col_idx
while temp:
quotient, remainder = divmod(temp, 26)
# check for exact division and borrow if needed
if remainder == 0:
quotient -= 1
remainder = 26
ordinals.append(remainder + 64)
temp = quotient
ordinals.reverse()
return ''.join([chr(ordinal) for ordinal in ordinals])