Thanks for you reply. I cannot understand the design of `org-src-preserve-indentation`.
Setting it to `nil` cause what described in my previous mail.
Setting it to `t` lose the leading two spaces indentation/alignment in the origin org buffer.
If it is `nil`, why inserting 2 leading spaces to the code in the org buffer except the line containing only spaces?
How can I get
a = 1
b = 2
for i in range(10):
# 6 spaces before '#'
after exit `org-edit-special` ?