This is neat! @phracek care to take a look?

@dhodovsk It seem to be working but format is not proper. I would prefer to keep formating

data:
api:
rpms: [source-to-image-1.0.9-2.fc25.x86_64]
components:
rpms:
golang-github-fsouza-go-dockerclient-devel-0.2.1-18.git2350d7b.fc26.noarch: {
rationale: Build dependency.}
golang-github-golang-glog-devel-0-0.14.gitfca8c88.fc26.noarch: {rationale: Build dependency.}
golang-github-spf13-cobra-devel-0-0.18.git8e91712.fc26.noarch: {rationale: Build dependency.}
golang-github-spf13-pflag-devel-0-0.17.gitc7e63cf.fc26.noarch: {rationale: Build dependency.}
dependencies:
buildrequires: {common-build-dependencies: f26}
requires: {base-runtime: f26, container-runtime: f26, shared-userspace: f26}
description: A tool for building artifacts from source and injecting into docker images
filter:
rpms: [golang-github-fsouza-go-dockerclient-devel-0.2.1-18.git2350d7b.fc26.noarch,
golang-github-spf13-cobra-devel-0-0.18.git8e91712.fc26.noarch, golang-github-spf13-pflag-devel-0-0.17.gitc7e63cf.fc26.noarch,
golang-github-golang-glog-devel-0-0.14.gitfca8c88.fc26.noarch]
license:
content: [ASL 2.0]
module: [MIT]
summary: A tool for building artifacts from source and injecting into docker images
document: modulemd
version: 1

The formatting functionality is managed by modulemd python module. The issue was discussed here: https://pagure.io/modulemd/pull-request/32

@phracek Please try again, I needed to explicitly specify str type of input, now it should work.