While trying to add a package to compression.scm, I just added the line
  #:use-module (gnu packages python)

This results in the following error:
Backtrace:
In ice-9/eval.scm:
 392: 19 [eval # ()]
In ice-9/boot-9.scm:
2667: 18 [define-module* (gnu packages compression) #:filename ...]
2642: 17 [resolve-imports (# # # # ...)]
2580: 16 [resolve-interface (gnu packages python) #:select ...]
2505: 15 [#<procedure 2698940 at ice-9/boot-9.scm:2493:4 (name #:optional 
autoload version #:key ensure)> # ...]
2772: 14 [try-module-autoload (gnu packages python) #f]
2111: 13 [save-module-excursion #<procedure 2e5b900 at 
ice-9/boot-9.scm:2773:17 ()>]
2783: 12 [#<procedure 2e5b900 at ice-9/boot-9.scm:2773:17 ()>]
In unknown file:
   ?: 11 [primitive-load-path "gnu/packages/python" #f]
In gnu/packages/python.scm:
  20: 10 [#<procedure 2e685c0 ()>]
In ice-9/boot-9.scm:
2667: 9 [define-module* (gnu packages python) #:filename ...]
2642: 8 [resolve-imports ((# # #) (#) (#) (#) ...)]
2580: 7 [resolve-interface (gnu packages base) #:select ...]
2505: 6 [#<procedure 2698940 at ice-9/boot-9.scm:2493:4 (name #:optional 
autoload version #:key ensure)> # ...]
2772: 5 [try-module-autoload (gnu packages base) #f]
2111: 4 [save-module-excursion #<procedure 2e6b6c0 at 
ice-9/boot-9.scm:2773:17 ()>]
2783: 3 [#<procedure 2e6b6c0 at ice-9/boot-9.scm:2773:17 ()>]
In unknown file:
   ?: 2 [primitive-load-path "gnu/packages/base" #f]
In gnu/packages/base.scm:
1055: 1 [#<procedure 2ecc020 ()>]
In ice-9/boot-9.scm:
 106: 0 [#<procedure 2825b40 at ice-9/boot-9.scm:97:6 (thrown-k . args)> 
unbound-variable ...]

ice-9/boot-9.scm:106:20: In procedure #<procedure 2825b40 at 
ice-9/boot-9.scm:97:6 (thrown-k . args)>:
ice-9/boot-9.scm:106:20: In procedure module-lookup: Unbound variable: gzip


In algebra.scm, for instance, there is no problem. And it is also not a 
clash with the variable gzip in compression.scm, because renaming it does 
not help.

Andreas