def rename_as_PC_columns(df, PC_axis_one=None, PC_axis_two=None):
	"""
	Rename pandas DataFrame column names as PC1, PC2, ...
	"""
	# Special case for environmental projection df
	# It needs to be hardcoded because of the way df is created (refer to 'project_env_metadata_to_ordination()'')
	if(PC_axis_one is not None and PC_axis_two is not None):
		new_col_names = ['PC' + str(PC_axis_one), 'PC' + str(PC_axis_two)]
		df.columns = new_col_names

		return df

	num_col = df.shape[1]
	if(num_col == 0):
		raise ValueError("Specified dataframe has zero columns...")

	new_col_names = ['PC' + str(i) for i in range(1, num_col+1)]
	df.columns = new_col_names

	return df