Lazy load yubikey module to avoid lib errors when not in use

src/gam.spec

@@ -16,8 +16,12 @@ extra_files += [('cbcm-v1.1beta1.json', '.')]
 extra_files += [('contactdelegation-v1.json', '.')]
 extra_files += [('versionhistory-v1.json', '.')]
 
+hidden_imports = [
+     'gam.auth.yubikey',
+     ]
+
 a = Analysis(['gam/__main__.py'],
-             hiddenimports=[],
+             hiddenimports=hidden_imports,
              hookspath=None,
              excludes=['FixTk', 'tcl', 'tk', '_tkinter', 'tkinter', 'Tkinter'],
              datas=extra_files,

src/gam/__init__.py

@@ -46,7 +46,6 @@ from cryptography.x509.oid import NameOID
 
 import gam.auth.oauth
 from gam import auth
-from gam.auth import yubikey
 from gam import controlflow
 from gam import display
 from gam import fileutils
@@ -84,6 +83,7 @@ from gam import transport
 from gam import utils
 from gam.var import *
 
+yubikey = utils.LazyLoader('yubikey', globals(), 'gam.auth.yubikey')
 from passlib.hash import sha512_crypt
 
 if platform.system() == 'Linux':

src/gam/auth/__init__.py

@@ -6,8 +6,9 @@ import os
 from google.auth.jwt import Credentials as JWTCredentials
 
 import gam
+from gam import utils
+
 from gam.auth import oauth
-from gam.auth import yubikey
 from gam.var import _FN_OAUTH2_TXT
 from gam.var import _FN_OAUTH2SERVICE_JSON
 from gam.var import GC_OAUTH2_TXT
@@ -15,6 +16,7 @@ from gam.var import GC_OAUTH2SERVICE_JSON
 from gam.var import GC_ENABLE_DASA
 from gam.var import GC_Values
 
+yubikey = utils.LazyLoader('yubikey', globals(), 'gam.auth.yubikey')
 # TODO: Move logic that determines file name into this module. We should be able
 # to discover the file location without accessing a private member or waiting
 # for a global initialization.

src/gam/utils.py

@@ -1,3 +1,7 @@
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
 import datetime
 import re
 import sys
@@ -5,8 +9,10 @@ import time
 from hashlib import md5
 from html.entities import name2codepoint
 from html.parser import HTMLParser
+import importlib
 import json
 import dateutil.parser
+import types
 
 from gam import controlflow
 from gam import fileutils
@@ -14,6 +20,41 @@ from gam import transport
 from gam.var import *
 
 
+class LazyLoader(types.ModuleType):
+  """Lazily import a module, mainly to avoid pulling in large dependencies.
+
+  `contrib`, and `ffmpeg` are examples of modules that are large and not always
+  needed, and this allows them to only be loaded when they are used.
+  """
+
+  # The lint error here is incorrect.
+  def __init__(self, local_name, parent_module_globals, name):  # pylint: disable=super-on-old-class
+    self._local_name = local_name
+    self._parent_module_globals = parent_module_globals
+
+    super(LazyLoader, self).__init__(name)
+
+  def _load(self):
+    # Import the target module and insert it into the parent's namespace
+    module = importlib.import_module(self.__name__)
+    self._parent_module_globals[self._local_name] = module
+
+    # Update this object's dict so that if someone keeps a reference to the
+    #   LazyLoader, lookups are efficient (__getattr__ is only called on lookups
+    #   that fail).
+    self.__dict__.update(module.__dict__)
+
+    return module
+
+  def __getattr__(self, item):
+    module = self._load()
+    return getattr(module, item)
+
+  def __dir__(self):
+    module = self._load()
+    return dir(module)
+
+
 class _DeHTMLParser(HTMLParser):
 
     def __init__(self):