upgrade syntax to py37+ and autoconvert some f-strings. add tox synta…

…x-upgrade task.

glom/__init__.py

@@ -1,4 +1,3 @@
-
 from glom.core import (glom,
                        Fill,
                        Auto,

glom/__main__.py

@@ -1,4 +1,3 @@
-
 from glom.cli import console_main
 
 if __name__ == '__main__':

glom/cli.py

@@ -28,7 +28,6 @@
 """
 
 
-from __future__ import print_function
 
 import os
 import ast
@@ -65,7 +64,7 @@ def glom_cli(target, spec, indent, debug, inspect):
     try:
         result = glom.glom(target, spec)
     except GlomError as ge:
-        print('%s: %s' % (ge.__class__.__name__, ge))
+        print(f'{ge.__class__.__name__}: {ge}')
         return 1
 
     if not indent:
@@ -170,10 +169,10 @@ def mw_get_target(next_, posargs_, target_file, target_format, spec_file, spec_f
         raise UsageError('expected spec file or spec argument, not both')
     elif spec_file:
         try:
-            with open(spec_file, 'r') as f:
+            with open(spec_file) as f:
                 spec_text = f.read()
-        except IOError as ose:
-            raise UsageError('could not read spec file %r, got: %s' % (spec_file, ose))
+        except OSError as ose:
+            raise UsageError(f'could not read spec file {spec_file!r}, got: {ose}')
 
     if not spec_text:
         spec = Path()
@@ -195,9 +194,9 @@ def mw_get_target(next_, posargs_, target_file, target_format, spec_file, spec_f
         target_text = sys.stdin.read()
     elif target_file:
         try:
-            target_text = open(target_file, 'r').read()
-        except IOError as ose:
-            raise UsageError('could not read target file %r, got: %s' % (target_file, ose))
+            target_text = open(target_file).read()
+        except OSError as ose:
+            raise UsageError(f'could not read target file {target_file!r}, got: {ose}')
     elif not target_text and not isatty(sys.stdin):
         target_text = sys.stdin.read()
 
@@ -218,7 +217,7 @@ def _from_glom_import_star():
 
 def _eval_python_full_spec(py_text):
     name = '__cli_glom_spec__'
-    code_str = '%s = %s' % (name, py_text)
+    code_str = f'{name} = {py_text}'
     env = _from_glom_import_star()
     spec = _compile_code(code_str, name=name, env=env)
     return spec