fix: environment variable affect initial setup macOS/win (#956)

cibuildwheel/windows.py

@@ -157,31 +157,6 @@ def setup_python(
     )
     env["PIP_DISABLE_PIP_VERSION_CHECK"] = "1"
 
-    # update env with results from CIBW_ENVIRONMENT
-    env = environment.as_dictionary(prev_environment=env)
-
-    # for the logs - check we're running the right version of python
-    call(["where", "python"], env=env)
-    call(["python", "--version"], env=env)
-    call(["python", "-c", "\"import struct; print(struct.calcsize('P') * 8)\""], env=env)
-    where_python = (
-        subprocess.run(
-            ["where", "python"],
-            env=env,
-            universal_newlines=True,
-            check=True,
-            stdout=subprocess.PIPE,
-        )
-        .stdout.splitlines()[0]
-        .strip()
-    )
-    if where_python != str(installation_path / "python.exe"):
-        print(
-            "cibuildwheel: python available on PATH doesn't match our installed instance. If you have modified PATH, ensure that you don't overwrite cibuildwheel's entry or insert python above it.",
-            file=sys.stderr,
-        )
-        sys.exit(1)
-
     log.step("Installing build tools...")
 
     # Install pip
@@ -230,6 +205,32 @@ def setup_python(
         cwd=CIBW_INSTALL_PATH,
     )
 
+    # update env with results from CIBW_ENVIRONMENT
+    env = environment.as_dictionary(prev_environment=env)
+
+    # check what Python version we're on
+    call(["where", "python"], env=env)
+    call(["python", "--version"], env=env)
+    call(["python", "-c", "\"import struct; print(struct.calcsize('P') * 8)\""], env=env)
+    where_python = (
+        subprocess.run(
+            ["where", "python"],
+            env=env,
+            universal_newlines=True,
+            check=True,
+            stdout=subprocess.PIPE,
+        )
+        .stdout.splitlines()[0]
+        .strip()
+    )
+    if where_python != str(installation_path / "python.exe"):
+        print(
+            "cibuildwheel: python available on PATH doesn't match our installed instance. If you have modified PATH, ensure that you don't overwrite cibuildwheel's entry or insert python above it.",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+    # check what pip version we're on
     assert (installation_path / "Scripts" / "pip.exe").exists()
     where_pip = (
         subprocess.run(