bpo-37587: Make json.loads faster for long strings (GH-14752)

When scanning the string, most characters are valid, so
checking for invalid characters first means never needing
to check the value of strict on valid strings, and only
needing to check it on invalid characters when doing
non-strict parsing of invalid strings.

This provides a measurable reduction in per-character
processing time (~11% in the pre-merge patch testing).
(cherry picked from commit 8a758f5b99c5fc3fd32edeac049d7d4a4b7cc163)

Co-authored-by: Marco Paolini <mpaolini@users.noreply.github.com>

diff --git a/Misc/NEWS.d/next/Library/2019-07-13-16-02-48.bpo-37587.fd-1aF.rst b/Misc/NEWS.d/next/Library/2019-07-13-16-02-48.bpo-37587.fd-1aF.rst
new file mode 100644 (file)
index 0000000..80a89fe
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-07-13-16-02-48.bpo-37587.fd-1aF.rst
@@ -0,0 +1 @@
+Make json.loads faster for long strings. (Patch by Marco Paolini)

diff --git a/Modules/_json.c b/Modules/_json.c
index e3aa997598fc2efbc1b488a23a572b9bd30c491a..048a9654ce18cab84ae8b8c2ad96792a6b2be8fe 100644 (file)
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -439,7 +439,7 @@ scanstring_unicode(PyObject *pystr, Py_ssize_t end, int strict, Py_ssize_t *next
             if (c == '"' || c == '\\') {
                 break;
             }
-            else if (strict && c <= 0x1f) {
+            else if (c <= 0x1f && strict) {
                 raise_errmsg("Invalid control character at", pystr, next);
                 goto bail;
             }