how to make the first line by 2 ch?

[paopjian]

paragraph_format.first_line_indent can only set by direct numbers, in word for Chinese, the paragraph indentation special can set First line by 2 ch. I don't know how to make it.
I find CharacterUnitFirstLineIndent in VBA,but not find in python-docx
I find that w:firstLineChars can make "by" show the ch

[gc13141112]

The configuration "paragraph_format.first_line_chars_indent = 2 " is not working. How to set the scripts?