Use f-strings

Now that minimum python supported is 3.6, we can use f-strings !

test/12_dependency_versions/cibuildwheel_test.py

@@ -44,11 +44,11 @@ def test_pinned_versions(python_version):
     constraint_versions = get_versions_from_constraint_file(constraint_file)
 
     for package in ['pip', 'setuptools', 'wheel', 'virtualenv']:
-        env_name = 'EXPECTED_{}_VERSION'.format(package.upper())
+        env_name = f'EXPECTED_{package.upper()}_VERSION'
         build_environment[env_name] = constraint_versions[package]
 
     cibw_environment_option = ' '.join(
-        ['{}={}'.format(k, v) for k, v in build_environment.items()]
+        [f'{k}={v}' for k, v in build_environment.items()]
     )
 
     # build and test the wheels
@@ -100,11 +100,11 @@ def test_dependency_constraints_file(tmp_path, python_version):
     build_environment = {}
 
     for package_name, version in tool_versions.items():
-        env_name = 'EXPECTED_{}_VERSION'.format(package_name.upper())
+        env_name = f'EXPECTED_{package_name.upper()}_VERSION'
         build_environment[env_name] = version
 
     cibw_environment_option = ' '.join(
-        ['{}={}'.format(k, v) for k, v in build_environment.items()]
+        [f'{k}={v}' for k, v in build_environment.items()]
     )
 
     # build and test the wheels

test/shared/utils.py

@@ -110,7 +110,7 @@ def expected_wheels(package_name, package_version, manylinux_versions=None,
                 architectures.append('i686')
 
             platform_tags = [
-                '{}_{}'.format(manylinux_version, architecture)
+                f'{manylinux_version}_{architecture}'
                 for architecture in architectures
                 for manylinux_version in manylinux_versions
             ]
@@ -122,16 +122,13 @@ def expected_wheels(package_name, package_version, manylinux_versions=None,
                 platform_tags = ['win32']
 
         elif platform == 'macos':
-            platform_tags = ['macosx_{}_x86_64'.format(macosx_deployment_target.replace('.', '_'))]
+            platform_tags = [f'macosx_{macosx_deployment_target.replace(".", "_")}_x86_64']
 
         else:
             raise Exception('unsupported platform')
 
         for platform_tag in platform_tags:
-            wheels.append('{package_name}-{package_version}-{python_abi_tag}-{platform_tag}.whl'.format(
-                package_name=package_name, package_version=package_version,
-                python_abi_tag=python_abi_tag, platform_tag=platform_tag
-            ))
+            wheels.append(f'{package_name}-{package_version}-{python_abi_tag}-{platform_tag}.whl')
 
     if IS_WINDOWS_RUNNING_ON_TRAVIS:
         # Python 2.7 isn't supported on Travis.