refactor: remove redundant Python 2 code (#1155)

* Remove Python 2 code

* Upgrade Python syntax with pyupgrade

* Upgrade Python syntax with pyupgrade --py3-plus

* Upgrade Python syntax with pyupgrade --py36-plus

* Remove unused imports

3 files changed, 12 insertions, 14 deletions

diff --git a/perf/bug397.py b/perf/bug397.py
index 390741e5..18c979b8 100644
--- a/perf/bug397.py
+++ b/perf/bug397.py
@@ -10,7 +10,6 @@ Run this file two ways under coverage and see that the times are the same:
 Written by David MacIver as part of https://github.com/nedbat/coveragepy/issues/397
 
 """
-from __future__ import print_function
 
 import sys
 import random
@@ -52,4 +51,4 @@ if __name__ == '__main__':
         for d in data:
             hash_str(d)
         timing.append(1000000 * (time.time() - start) / len(data))
-    print("Runtime per example:", "%.2f +/- %.2f us" % (mean(timing), sd(timing)))
+    print("Runtime per example:", f"{mean(timing):.2f} +/- {sd(timing):.2f} us")
diff --git a/perf/perf_measure.py b/perf/perf_measure.py
index 652f0fa8..e8f9ea98 100644
--- a/perf/perf_measure.py
+++ b/perf/perf_measure.py
@@ -38,15 +38,15 @@ def child(line_count):
 def mk_main(file_count, call_count, line_count):
     lines = []
     lines.extend(
-        "import test{}".format(idx) for idx in range(file_count)
+        f"import test{idx}" for idx in range(file_count)
     )
     lines.extend(
-        "test{}.parent({}, {})".format(idx, call_count, line_count) for idx in range(file_count)
+        f"test{idx}.parent({call_count}, {line_count})" for idx in range(file_count)
     )
     return "\n".join(lines)
 
 
-class StressTest(object):
+class StressTest:
 
     def __init__(self):
         self.module_cleaner = SuperModuleCleaner()
@@ -55,7 +55,7 @@ class StressTest(object):
         self.module_cleaner.clean_local_file_imports()
 
         for idx in range(file_count):
-            make_file('test{}.py'.format(idx), TEST_FILE)
+            make_file(f'test{idx}.py', TEST_FILE)
         make_file('testmain.py', mk_main(file_count, call_count, line_count))
 
         # Run it once just to get the disk caches loaded up.
@@ -137,7 +137,7 @@ class StressTest(object):
                     yield kwargs['file_count'] * kwargs['call_count'] * kwargs['line_count']
 
         ops = sum(sum(operations(thing)) for thing in ["file", "call", "line"])
-        print("{:.1f}M operations".format(ops/1e6))
+        print(f"{ops/1e6:.1f}M operations")
 
     def check_coefficients(self):
         # For checking the calculation of actual stats:
@@ -161,14 +161,14 @@ class StressTest(object):
                     }
                     kwargs[thing+"_count"] = n
                     res = self._compute_overhead(**kwargs)
-                    per_thing.append(res.overhead / getattr(res, "{}s".format(thing)))
+                    per_thing.append(res.overhead / getattr(res, f"{thing}s"))
                     pct_thing.append(res.covered / res.baseline * 100)
 
-            out = "Per {}: ".format(thing)
+            out = f"Per {thing}: "
             out += "mean = {:9.3f}us, stddev = {:8.3f}us, ".format(
                 statistics.mean(per_thing)*1e6, statistics.stdev(per_thing)*1e6
             )
-            out += "min = {:9.3f}us, ".format(min(per_thing)*1e6)
+            out += f"min = {min(per_thing)*1e6:9.3f}us, "
             out += "pct = {:6.1f}%, stddev = {:6.1f}%".format(
                 statistics.mean(pct_thing), statistics.stdev(pct_thing)
             )
@@ -181,7 +181,7 @@ class StressTest(object):
 
 if __name__ == '__main__':
     with tempfile.TemporaryDirectory(prefix="coverage_stress_") as tempdir:
-        print("Working in {}".format(tempdir))
+        print(f"Working in {tempdir}")
         os.chdir(tempdir)
         sys.path.insert(0, ".")
 
diff --git a/perf/solve_poly.py b/perf/solve_poly.py
index 66231725..083dc544 100644
--- a/perf/solve_poly.py
+++ b/perf/solve_poly.py
@@ -10,7 +10,6 @@ import attr
 import itertools
 import numpy
 import scipy.optimize
-import sys
 
 
 def f(*args, simplify=False):
@@ -207,7 +206,7 @@ for row in INPUT.splitlines():
 #print('\n'.join(str(t) for t in inputs_outputs.items()))
 
 def calc_poly_coeff(poly, coefficients):
-    c_tuples = list(((c,) for c in coefficients))
+    c_tuples = list((c,) for c in coefficients)
     poly = list(f(*poly))
     poly = list(a + b for a, b in zip(c_tuples, poly))
     multiplied = list(m(*t) for t in poly)
@@ -241,7 +240,7 @@ with open('results', 'w') as f:
 
         coefficients = [int(round(x)) for x in c.x]
         terms = [''.join(t) for t in poly.terms]
-        message = "{}' = ".format(name)
+        message = f"{name}' = "
         message += ' + '.join("{}{}".format(coeff if coeff != 1 else '', term) for coeff, term in reversed(list(zip(coefficients, terms))) if coeff != 0)
         print(message)
         f.write(message)