Add module common code to allow it to be easier to indicate whether arguments are mutually exclusive, required in conjunction, or whether one of a list of arguments is required. This simplifies writing Python modules.

pip

@@ -90,7 +90,11 @@ def main():
         virtualenv=dict(default=None, required=False)
     )
 
-    module = AnsibleModule(argument_spec=arg_spec)
+    module = AnsibleModule(
+        argument_spec=arg_spec,
+        required_one_of=[['name','requirements']],
+        mutually_exclusive=[['name','requirements']],
+    )
 
     rc = 0
     err = ''
@@ -115,38 +119,19 @@ def main():
     command_map = dict(present='install', absent='uninstall', latest='install')
 
     if state == 'latest' and version is not None:
-        module.fail_json(msg='If `state` is set to `latest` the `version` '
-                             'parameter must not be specified.')
+        module.fail_json(msg='version is incompatible with state=latest')
 
     if state == 'latest' and requirements is not None:
-        module.fail_json(msg='If `state` is set to `latest` the `requirements` '
-                             'parameter must not be specified.')
-
-    if name is not None and '==' in name:
-        module.fail_json(msg='It looks like you specified the version number '
-                             'in the library name. Use the `version` parameter '
-                             'to specify version instead')
-
-    if version is not None and name is None:
-        module.fail_json(msg='The `version` parameter must be used with the '
-                             '`name` parameter and not with the `requirements` '
-                             'paramter')
-
-    if name is None and requirements is None:
-        module.fail_json(msg='You must specify a python library name via '
-                             'the `name` parameter or a requirements file via '
-                             'the `requirements` paramter')
-
-    if name and requirements:
-        module.fail_json(msg='Both `name` and `requirements` were specified. '
-                             'Specify only the python library name via the '
-                             '`name` parameter or a requirements file via the '
-                             '`requirements` parameter')
+        module.fail_json(msg='requirements is incompatible with state=latest')
+
+    if name is not None and '=' in name:
+        module.fail_json(msg='versions must be specified in the version= parameter')
 
     cmd = None
     installed = None
 
     if requirements:
+
         cmd = '%s %s -r %s --use-mirrors' % (pip, command_map[state], requirements)
         rc_pip, out_pip, err_pip = _run(cmd)
 
@@ -158,8 +143,8 @@ def main():
                    (not _did_install(out) and state == 'absent'))
 
     if name and state == 'latest':
-        cmd = '%s %s %s --upgrade' % (pip, command_map[state], name)
 
+        cmd = '%s %s %s --upgrade' % (pip, command_map[state], name)
         rc_pip, out_pip, err_pip = _run(cmd)
 
         rc += rc_pip
@@ -169,8 +154,8 @@ def main():
         changed = 'Successfully installed' in out_pip
 
     elif name:
-        installed = _is_package_installed(name, pip, version)
         
+        installed = _is_package_installed(name, pip, version)
         changed = ((installed and state == 'absent') or
                    (not installed and state == 'present'))
 
@@ -188,7 +173,6 @@ def main():
                 cmd = cmd + ' --use-mirrors'
 
             rc_pip, out_pip, err_pip = _run(cmd)
-
             rc  += rc_pip
             out += out_pip
             err += err_pip

yum

@@ -35,7 +35,6 @@ def is_installed(repoq, pkgspec, qf=def_qf):
     rc,out,err = run(cmd)
     if rc == 0:
         return [ p for p in out.split('\n') if p.strip() ]
-
     return []
 
 def is_available(repoq, pkgspec, qf=def_qf):
@@ -43,10 +42,8 @@ def is_available(repoq, pkgspec, qf=def_qf):
     rc,out,err = run(cmd)
     if rc == 0:
         return [ p for p in out.split('\n') if p.strip() ]
-
     return []
 
-
 def is_update(repoq, pkgspec, qf=def_qf):
     cmd = repoq + ["--pkgnarrow=updates", "--qf", qf, pkgspec]
     rc,out,err = run(cmd)
@@ -55,17 +52,14 @@ def is_update(repoq, pkgspec, qf=def_qf):
 
     return []
 
-
 def what_provides(repoq, req_spec, qf=def_qf):
     cmd = repoq + ["--qf", qf, "--whatprovides", req_spec]
     rc,out,err = run(cmd)
     ret = []
     if rc == 0:
         ret = set([ p for p in out.split('\n') if p.strip() ])
-
     return ret
 
-
 def pkg_to_dict(pkgstr):
     if pkgstr.strip():
         n,e,v,r,a,repo = pkgstr.split('|')
@@ -95,7 +89,6 @@ def repolist(repoq, qf="%{repoid}"):
     ret = []
     if rc == 0:
         ret = set([ p for p in out.split('\n') if p.strip() ])
-
     return ret
 
 def list_stuff(conf_file, stuff):
@@ -128,7 +121,6 @@ def run(command):
         rc = 1
         err = traceback.format_exc()
         out = ''
-
         if out is None:
             out = ''
         if err is None:
@@ -429,15 +421,13 @@ def main():
             state=dict(default='installed', choices=['absent','present','installed','removed','latest']),
             list=dict(),
             conf_file=dict(default=None),
-        )
+        ),
+        required_one_of = [['pkg','list']],
+        mutually_exclusive = [['pkg','list']]
     )
 
     params = module.params
 
-
-    if params['list'] and params['pkg']:
-        module.fail_json(msg="expected 'list=' or 'name=', but not both")
-
     if params['list']:
         if not os.path.exists(repoquery):
             module.fail_json(msg="%s is required to use list= with this module. Please install the yum-utils package." % repoquery)
@@ -446,9 +436,6 @@ def main():
 
     else:
         pkg = params['pkg']
-        if pkg is None:
-            module.fail_json(msg="expected 'list=' or 'name='")
-        else:
         state = params['state']
         res = ensure(module, state, pkg, params['conf_file'])
         module.fail_json(msg="we should never get here unless this all failed", **res)