Returns the column (as index) containing the IPA data based on the
		header (the first line of the data file). Raises ValueError otherwise.

		If self.ipa_col is a string, it is assumed to be the column's name or
		index. Otherwise, several common IPA column names are tried.

def _infer_ipa_col(self, header):
		"""
		Returns the column (as index) containing the IPA data based on the
		header (the first line of the data file). Raises ValueError otherwise.

		If self.ipa_col is a string, it is assumed to be the column's name or
		index. Otherwise, several common IPA column names are tried.
		"""
		if self.ipa_col and isinstance(self.ipa_col, str):
			if self.ipa_col in header:
				return header.index(self.ipa_col)

			try:
				ipa_col = int(self.ipa_col)
			except ValueError: pass
			else:
				return ipa_col

			raise ValueError('Could not find column: {}'.format(self.ipa_col))

		pot = []

		for index, col_name in enumerate(header):
			col_name = col_name.lower()
			for name in IPA_COL_NAMES:
				if col_name.startswith(name):
					pot.append(index)

		if len(pot) == 0:
			raise ValueError('Could not find an IPA column')
		elif len(pot) > 1:
			raise ValueError('Could not decide which is the IPA column')

		return pot[0]