Fixes import, linter and comments

Also adds sympy to ignore list:
```
Please install the mpmath package with a version >= 0.19
```

Author: AndreMiras

ci/constants.py

@@ -57,6 +57,8 @@ class TargetPython(Enum):
     'pyzmq',
     'secp256k1',
     'shapely',
+    # mpmath package with a version >= 0.19 required
+    'sympy',
     'twisted',
     'vlc',
     'websocket-client',
@@ -93,6 +95,8 @@ class TargetPython(Enum):
     'pyjnius', 'pyopenal',
     # SyntaxError: invalid syntax (Python2)
     'storm',
+    # mpmath package with a version >= 0.19 required
+    'sympy',
     'vlc',
 ])
 # to be created via https://github.com/kivy/python-for-android/issues/1514

pythonforandroid/recipes/sympy/__init__.py

@@ -1,16 +1,16 @@
 
-from pythonforandroid.toolchain import PythonRecipe
+from pythonforandroid.recipe import PythonRecipe
 
 
 class SympyRecipe(PythonRecipe):
     version = '1.1.1'
     url = 'https://github.com/sympy/sympy/releases/download/sympy-{version}/sympy-{version}.tar.gz'
 
-    # depends = [('python2', 'python3crystax'), 'setuptools']
     depends = [('python2', 'python3crystax'), 'mpmath']
 
     call_hostpython_via_targetpython = True
 
     patches = ['fix_timeutils.patch', 'fix_pretty_print.patch']
 
+
 recipe = SympyRecipe()