[python]: swagger v3 fails to generate client

Description

Trying out the swagger v3 to generate a python client but i am hitting basic issue while executing codegen. Can someone please help?

Swagger-codegen version

java -jar swagger-codegen-cli-3.0.0-20180112.231857-20.jar version
3.0.0-SNAPSHOT

Swagger declaration file content or url

On first attempt i hit a missing .swagger-codegen-ignore file. Had never faced this issue with v2 so am not sure of the need of this file. I tried to just create a dummy ignore file but then i see missing swagger input of config even though i had the config file mentioned with -c option.

$ java -jar swagger-codegen-cli-3.0.0-20180112.231857-20.jar generate -i restapi-v3-3.yaml -DapiTests=false,apiDocs=false,modelTests=false,modelDocs=false -c config.json -l python -o v3-client1
usage: swagger-codegen generate [-h] [-v []] [-l] [-o] [-i] [-t] [-a] [-c] [-s] [--api-package] [--model-package] [--model-name-prefix] [--model-name-suffix] [--instantiation-types [ [ ...]]]
[--type-mappings [ [ ...]]] [--additional-properties [ [ ...]]] [--import-mappings [ [ ...]]] [--invoker-package] [--group-id] [--artifact-id] [--artifact-version]
[--library] [--git-user-id] [--git-repo-id] [--release-note] [--http-user-agent] [--reserved-words-mappings [ [ ...]]] [--ignore-file-override] [--remove-operation-id-prefix]
[-u]
swagger-codegen: error: unrecognized arguments: '-DapiTests=false,apiDocs=false,modelTests=false,modelDocs=false'

$ java -jar swagger-codegen-cli-3.0.0-20180112.231857-20.jar generate -i restapi-v3-3.yaml -c config.json -l python -o v3-client1
[Thread-1] INFO io.swagger.codegen.ignore.CodegenIgnoreProcessor - No .swagger-codegen-ignore file found.
Exception in thread "Thread-1" java.lang.RuntimeException: missing swagger input or config!
at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:713)
at io.swagger.codegen.cmd.Generate.run(Generate.java:312)
at java.lang.Thread.run(Thread.java:745)

$ java -jar swagger-codegen-cli-3.0.0-20180112.231857-20.jar generate -i restapi-v3-3.yaml -c config.json -l python -o v3-client1
[Thread-1] INFO io.swagger.codegen.ignore.CodegenIgnoreProcessor - No .swagger-codegen-ignore file found.
Exception in thread "Thread-1" java.lang.RuntimeException: missing swagger input or config!
at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:713)
at io.swagger.codegen.cmd.Generate.run(Generate.java:312)
at java.lang.Thread.run(Thread.java:745)

$ java -jar swagger-codegen-cli-3.0.0-20180112.231857-20.jar generate -i restapi-v3-3.yaml -c config.json -l python -o v3-client1
Exception in thread "Thread-1" java.lang.RuntimeException: missing swagger input or config!
at io.swagger.codegen.DefaultGenerator.generate(DefaultGenerator.java:713)
at io.swagger.codegen.cmd.Generate.run(Generate.java:312)
at java.lang.Thread.run(Thread.java:745)

$ cat config.json
{
"packageName" : "xyz",
"packageVersion" : "1.0.0"
}

Command line used for generation

see above.

Start with the reported command, restapi-v3-3.yaml, config.json, and the stack trace in io.swagger.codegen.cmd.Generate.run and io.swagger.codegen.DefaultGenerator.generate. Reproduce the missing swagger input or config error with the listed CLI invocation, then confirm that a Python client can be generated using the supplied files and options.