Patching setup.py for installation without pip for Spack

CHANGELOG.md

@@ -4,6 +4,7 @@ All notable changes to this project will be documented in this file.
 
 ## latest
 
+* `packaging` and `pip` are now optional dependencies. https://github.com/precice/python-bindings/pull/63
 * Feature: Bindings are now available via Spack. https://github.com/spack/spack/pull/19558
 * Bugfix: Bindings also support empty read/write data for block read/write operations (like C++ preCICE API). https://github.com/precice/python-bindings/pull/69
 

README.md

@@ -17,7 +17,8 @@ This package provides python language bindings for the C++ library [preCICE](htt
 
 # Installing the package
 
-We recommend using pip3 (version 19.0 or newer) for the sake of simplicity. You can check your pip3 version via `pip3 --version`. To update pip3, use the following line:
+We recommend using pip3 (version 19.0.0 or newer required) for the sake of simplicity. You can check your pip3 version via `pip3 --version`. To update pip3, use the following line:
+
 ```
 $ pip3 install --upgrade pip
 ```
@@ -171,39 +172,6 @@ There are two possible reasons, why preCICE is not found:
 
 In case the compilation fails with `shared_ptr.pxd not found` messages, check if you use the latest version of Cython.
 
-### Version of pip3 is too old
-
-If you see the following error
-```
-error: option --single-version-externally-managed not recognized
-```
-your version of pip might be too old. Please update pip and try again. One possible way for updating pip is to run the following commands:
-```
-wget -q https://bootstrap.pypa.io/get-pip.py -O get-pip.py && python3 get-pip.py
-```
-*Be aware that `python3 get-pip.py` might require root privileges.*
-
-Check your version of pip via `pip3 --version`. For version 8.1.1 and 9.0.1 we know that this problem occurs. *Remark:* you get versions 8.1.1 of pip if you use `sudo apt install python3-pip` on Ubuntu 16.04 (pip version 9.0.1 on Ubuntu 18.04)
-
-### Build-time dependencies (Cython, numpy...) defined in `pyproject.toml` are not installed automatically
-
-If you see the following error
-```
-Collecting pyprecice
-  Using cached https://files.pythonhosted.org/packages/a6/fb/66f78168394afa2adca62ecd9079a98e741fbf3c6a96845719641ea27912/pyprecice-2.0.0.1.tar.gz
-    Complete output from command python setup.py egg_info:
-    Traceback (most recent call last):
-      File "<string>", line 1, in <module>
-      File "/tmp/pip-build-ebyoc0sq/pyprecice/setup.py", line 7, in <module>
-        from Cython.Distutils.extension import Extension
-    ModuleNotFoundError: No module named 'Cython'
-```
-your pip might be too old and therefore it does not use the information from `pyproject.toml`. You can update your pip via
-```
-pip3 install --upgrade pip
-```
-then try to install `pyprecice`, again.
-
 ### `Python.h` missing
 
 ```

pyproject.toml

@@ -1,3 +1,3 @@
 [build-system]
 # PEP 518 - minimum build system requirements
-requires = ["setuptools", "wheel", "Cython>=0.29", "packaging", "pip", "numpy", "mpi4py"]
+requires = ["setuptools", "wheel", "Cython>=0.29", "packaging", "pip>=19.0.0", "numpy", "mpi4py"]

setup.py

@@ -1,8 +1,45 @@
 import os
+import sys
 import warnings
-from packaging import version
 import versioneer
-import pip
+
+uses_pip = "pip" in __file__
+
+# check whether pip is used for installation. If pip is not used, dependencies defined in pyproject.toml might be
+# missing.
+if not uses_pip:
+    warnings.warn("It looks like you are not using pip for installation. Installing the package via 'pip3 install "
+                  "--user .' is recommended. You can still use 'python3 setup.py install --user', if you want and if "
+                  "the bindings work correctly, you do not have to worry. However, if you face problems during "
+                  "installation or running pyprecice, this means that you have to make sure that all dependencies are "
+                  "installed correctly and repeat the installation of pyprecice. Refer to pyproject.toml for a list "
+                  "of dependencies.")
+
+if uses_pip:
+    # If installed with pip we need to check its version
+    try:
+        import pip
+    except ModuleNotFoundError:
+        raise Exception("It looks like you are trying to use pip for installation of the package, but pip is not "
+                        "installed on your system (or cannot be found). This can lead to problems with missing "
+                        "dependencies. Please make sure that pip is discoverable. Try python3 -c 'import pip'. "
+                        "Alternatively, you can also run python3 setup.py install --user.")
+    try:
+        from packaging import version
+    except ModuleNotFoundError:
+        warnings.warn("It looks like you are trying to use pip for installation of the package. Please install, "
+                      "the module packaging by running 'pip3 install --user packaging', since it is needed to perform "
+                      "additional security checks. You can continue installation. However, if you face problems when "
+                      "installing or running pyprecice, it might be a good idea to install packaging to enable "
+                      "additional checks.")        
+    if "pip" in sys.modules and "packaging" in sys.modules:
+        if version.parse(pip.__version__) < version.parse("19.0"):
+            # version 19.0 is required, since we are using pyproject.toml for definition of build-time depdendencies.
+            # See https://pip.pypa.io/en/stable/news/#id209
+            raise Exception("You are using pip version {}. However, pip version >= 19.0 is required. Please upgrade "
+                            "your pip installation via 'pip3 install --upgrade pip'. You might have to add the --user"
+                            " flag.".format(pip.__version__))
+
 from setuptools import setup
 from setuptools import Command
 from setuptools.command.test import test
@@ -12,22 +49,6 @@
 from Cython.Build import cythonize
 import numpy
 
-if version.parse(pip.__version__) < version.parse("19.0"):
-    # version 19.0 is required, since we are using pyproject.toml for definition of build-time depdendencies. See
-    # https://pip.pypa.io/en/stable/news/#id209
-    warnings.warn(
-        "You are using pip version {}. However, pip version > 19.0 is recommended. You can continue with the "
-        "installation, but installation problems can occour. Please refer to "
-        "https://github.com/precice/python-bindings#build-time-dependencies-cython-numpy-defined-in-pyprojecttoml-are"
-        "-not-installed-automatically for help.".format(
-            pip.__version__))
-
-if version.parse(pip.__version__) < version.parse("10.0.1"):
-    warnings.warn(
-        "You are using pip version {}. However, pip version > 10.0.1 is required. If you continue with installation "
-        "it is likely that you will face an error. See "
-        "https://github.com/precice/python-bindings#version-of-pip3-is-too-old".format(
-            pip.__version__))
 
 # name of Interfacing API
 APPNAME = "pyprecice"