BLD: Remove hard installation dep

.flake8

@@ -17,5 +17,8 @@ ignore =
     # Useful to ignore for "import keras.backend as K"
     N812
 
-#imported but unused in __init__.py, that's ok.
-per-file-ignores = **/__init__.py:F401
+per-file-ignores =
+    # imported but unused in __init__.py, that's ok.
+    **/__init__.py:F401
+    # import not at top okay due to TF installation check
+    tensorflow_addons/__init__.py:F401,E402

build_deps/build-requirements.txt

@@ -0,0 +1 @@
+tensorflow==2.1.0

build_deps/check_deps.py

@@ -26,8 +26,9 @@ def check_dependencies(requirement_file_name):
     except DistributionNotFound as e:
         print(e)
         sys.exit(1)
-    sys.exit(0)
 
 
 if __name__ == "__main__":
     check_dependencies("requirements.txt")
+    check_dependencies("build_deps/build-requirements.txt")
+    sys.exit(0)

configure.py

@@ -86,12 +86,12 @@ def generate_shared_lib_name(namespec):
 print()
 print("Configuring TensorFlow Addons to be built from source...")
 
-_PIP_INSTALL_OPTS = "--upgrade"
+_PIP_INSTALL_OPTS = ["--upgrade"]
 parser = argparse.ArgumentParser()
 parser.add_argument("--quiet", action="store_true", help="Give less output.")
 args = parser.parse_args()
 if args.quiet:
-    _PIP_INSTALL_OPTS += " --quiet"
+    _PIP_INSTALL_OPTS.append("--quiet")
 
 # Any python git package would be preferable
 # _BRANCH=subprocess.check_output(["git", "rev-parse", "--abbrev-ref", "HEAD"]).decode('UTF-8').strip()
@@ -100,6 +100,9 @@ def generate_shared_lib_name(namespec):
 with open("requirements.txt") as f:
     _REQUIRED_PKG = f.read().splitlines()
 
+with open("build_deps/build-requirements.txt") as f:
+    _REQUIRED_PKG.extend(f.read().splitlines())
+
 print()
 print("> TensorFlow Addons will link to the framework in a pre-installed TF pacakge...")
 print("> Checking installed packages in {}".format(_PYTHON_PATH))
@@ -112,17 +115,10 @@ def generate_shared_lib_name(namespec):
     )
     if reply in ("y", "Y"):
         print("> Installing...")
-        subprocess.check_call(
-            [
-                _PYTHON_PATH,
-                "-m",
-                "pip",
-                "install",
-                _PIP_INSTALL_OPTS,
-                "-r",
-                "requirements.txt",
-            ]
-        )
+        install_cmd = [_PYTHON_PATH, "-m", "pip", "install"]
+        install_cmd.extend(_PIP_INSTALL_OPTS)
+        install_cmd.extend(_REQUIRED_PKG)
+        subprocess.check_call(install_cmd)
     else:
         print("> Exiting...")
         sys.exit()

requirements.txt

@@ -1,2 +1 @@
-tensorflow==2.1.0
 typeguard

tensorflow_addons/__init__.py

@@ -14,6 +14,47 @@
 # ==============================================================================
 """Useful extra functionality for TensorFlow maintained by SIG-addons."""
 
+
+# Ensure TensorFlow is importable and its version is sufficiently recent. This
+# needs to happen before anything else, since the imports below will try to
+# import tensorflow, too.
+def _ensure_tf_install():
+    """Attempt to import tensorflow, and ensure its version is sufficient.
+    Raises:
+      ImportError: if either tensorflow is not importable or its version is
+      inadequate.
+    """
+    try:
+        import tensorflow as tf
+    except ImportError:
+        # Print more informative error message, then reraise.
+        print(
+            "\n\nFailed to import TensorFlow. Please note that TensorFlow is"
+            " not installed by default when you install TensorFlow Addons.\n\n"
+        )
+        raise
+
+    import distutils.version
+
+    #
+    # Update this whenever we need to depend on a newer TensorFlow release.
+    #
+    required_tensorflow_version = "2.1.0"
+
+    if distutils.version.LooseVersion(tf.__version__) < distutils.version.LooseVersion(
+        required_tensorflow_version
+    ):
+        raise ImportError(
+            "This version of TensorFlow Addons requires TensorFlow "
+            "version >= {required}; Detected an installation of version "
+            "{present}. Please upgrade TensorFlow to proceed.".format(
+                required=required_tensorflow_version, present=tf.__version__
+            )
+        )
+
+
+_ensure_tf_install()
+
 # Local project imports
 from tensorflow_addons import activations
 from tensorflow_addons import callbacks