Provide mock 'dicom' import with helpful transition information (#585)

* Provide mock 'dicom' import with helpful transition information

* pep-8 fix

dicom.py

@@ -0,0 +1,11 @@
+msg = """
+Pydicom via 'import dicom' has been removed in pydicom version 1.0.
+Please install the `dicom` package to restore function of code relying
+on pydicom 0.9.9 or earlier. E.g. `pip install dicom`.
+Alternatively, most code can easily be converted to pydicom > 1.0 by
+changing import lines from 'import dicom' to 'import pydicom'.
+See the Transition Guide at
+https://pydicom.github.io/pydicom/stable/transition_to_pydicom1.html.
+"""
+
+raise ImportError(msg)

pydicom/_version.py

@@ -1,6 +1,6 @@
 """Pure python package for DICOM medical file reading and writing."""
 import re
 
-__version__ = '1.0.1'
+__version__ = '1.0.2'
 __version_info__ = tuple(
     re.match(r'(\d+\.\d+\.\d+).*', __version__).group(1).split('.'))

setup.cfg

@@ -1,5 +1,5 @@
 [bumpversion]
-current_version = 1.0.1
+current_version = 1.0.2
 tag = False
 parse = (?P<major>\d+)\.(?P<minor>\d+)\.(?P<patch>\d+)(\.(?P<release>[a-z]+)(?P<dev>\d+))?
 serialize = 

setup.py

@@ -6,9 +6,15 @@
 from glob import glob
 from setuptools import setup, find_packages
 
+have_dicom = True
+try:
+    import dicom
+except ImportError:
+    have_dicom = False
+
 # get __version__ from _version.py
 base_dir = os.path.dirname(os.path.realpath(__file__))
-ver_file = os.path.join(base_dir,'pydicom', '_version.py')
+ver_file = os.path.join(base_dir, 'pydicom', '_version.py')
 with open(ver_file) as f:
     exec(f.read())
 
@@ -34,6 +40,9 @@
 
 needs_pytest = {'pytest', 'test', 'ptr'}.intersection(sys.argv)
 pytest_runner = ['pytest-runner'] if needs_pytest else []
+_py_modules = []
+if not have_dicom:
+    _py_modules = ['dicom']
 
 CLASSIFIERS = [
     "License :: OSI Approved :: MIT License",
@@ -96,6 +105,7 @@ def data_files_inventory():
             keywords=KEYWORDS,
             classifiers=CLASSIFIERS,
             packages=find_packages(),
+            py_modules=_py_modules,
             package_data=PACKAGE_DATA,
             include_package_data=True,
             install_requires=REQUIRES,