Let me understand the bug: 1. When a Unicode method name like `u'POST'` is passed to `requests.request()`, it eventually gets set as `req.method = method.upper()` which keeps it as Unicode. 2. Later, when httplib tries to send the request, it concatenates the message body (bytes) with headers (which contain the method). If the method is Unicode, Python 2 tries to encode it using ASCII, but the binary body may contain non-ASCII bytes, causing a `UnicodeDecodeError`. The fix should be to ensure the method is always a byte string (str) in Python 2, not a unicode string. Let me look at the relevant source files.

Let me analyze the bug: 1. The issue is that when a Unicode method name like `u'POST'` is passed, it gets propagated through the code as a Unicode string. In Python 2, when this Unicode string eventually gets concatenated with byte strings (like the message body), Python tries to decode the byte string to Unicode using ASCII codec, which fails if the body contains non-ASCII bytes. 2. Looking at the code: In `sessions.py`, line ~313 (the `request` method): ```python req = Request( method = method.upper(), ... ) ``` And in `sessions.py`, line ~242 (the `prepare_request` method): ```python p.prepare( method=request.method.upper(), ... ) ``` And in `models.py`, `prepare_method`: ```python def prepare_method(self, method): """Prepares the given HTTP method.""" self.method = method if self.method is not None: self.method = self.method.upper() ``` The issue is that `method.upper()` on a Unicode string returns a Unicode string. This Unicode string stays Unicode all the way to httplib, where it causes a `UnicodeDecodeError` when concatenated with byte strings. The fix should ensure the method is always a native string (bytes in Python 2, str in Python 3). We need to convert it to a native string. Let me look at the `compat.py` to see what utilities are available.

Now I understand the issue clearly. In Python 2: - `str` is mapped to `unicode` (line: `str = unicode`) - `bytes` is mapped to `str` (the built-in byte string) - `builtin_str` is mapped to `str` (the built-in byte string) When `method.upper()` is called on a Unicode string, it returns a Unicode string. This Unicode method then gets passed to httplib, which eventually concatenates it with byte strings (like the body), causing a `UnicodeDecodeError`. The fix should be in `models.py` in the `prepare_method` method. We should convert the method to a native/builtin string (bytes in Py2, str in Py3). Let me also check the `sessions.py` lines that call `.upper()` on method: 1. `sessions.py` line ~313: `method = method.upper()` - but wait, this is `req = Request(method = method.upper(), ...)` - the Request object stores the method, then later `prepare_request` calls `p.prepare(method=request.method.upper(), ...)` which calls `prepare_method`. 2. `sessions.py` line ~242: `method=request.method.upper()` - this is in `prepare_request`. 3. `models.py` `prepare_method`: `self.method = self.method.upper()`. The best place to fix this is in `models.py`'s `prepare_method`, since that's the central place where the method is prepared. We should ensure that after calling `.upper()`, the method is converted to a native/builtin string. Let me also check `to_native_string` from utils:

Let me see the `to_native_string` function.

Let me read from the line number directly.

So `to_native_string` converts to the native string type (bytes in Py2, str in Py3). But wait, it has a bug too - in the `is_py2` branch, it calls `string.encode(encoding)`, but `string` would be a `str` (unicode) type in Py2. And in the `is_py3` branch, it calls `string.decode(encoding)`, but `string` would be `bytes` in Py3. This seems backwards... Actually wait, let me re-examine. In Py2: - `builtin_str` = `str` (the built-in byte string) - `str` = `unicode` So if `string` is already a `builtin_str` (byte string), return it as-is. If `string` is not a `builtin_str` (i.e., it's unicode), then in Py2, encode it to bytes: `string.encode(encoding)`. That seems correct for Py2. In Py3: - `builtin_str` = `str` - `str` = `str` So if `string` is already a `str`, return it. If it's not a `str` (i.e., it's `bytes`), decode it: `string.decode(encoding)`. Yes, that's correct. Now, the fix: In `models.py`, the `prepare_method` method should ensure the method is a native string. I can either: 1. Use `to_native_string` on the result 2. Just call `.upper()` and then convert to builtin_str Let me look at what the actual fix should be. The simplest fix is in `models.py`'s `prepare_method`: ```python def prepare_method(self, method): """Prepares the given HTTP method.""" self.method = method if self.method is not None: self.method = to_native_string(self.method.upper()) ``` Wait, but `to_native_string` is imported in models.py? Let me check the imports in models.py. From models.py imports: ```python from .utils import ( guess_filename, get_auth_from_url, requote_uri, stream_decode_response_unicode, to_key_val_list, parse_header_links, iter_slices, guess_json_utf, super_len, to_native_string) ``` Yes, `to_native_string` is already imported in `models.py`. But wait, I also need to check whether `prepare_method` is only called from `prepare` which is called from `prepare_request` in sessions.py. Let me also check if there are other places where the method is set. Looking at the code flow: 1. `Session.request()` creates a `Request` with `method = method.upper()` 2. `Session.prepare_request()` calls `p.prepare(method=request.method.upper(), ...)` 3. `PreparedRequest.prepare()` calls `self.prepare_method(method)` 4. `PreparedRequest.prepare_method()` does `self.method = self.method.upper()` The fix should be in `prepare_method` since that's the central place. But we could also fix it in sessions.py where `.upper()` is first called. Let me fix it in `prepare_method` in models.py as that's the most centralized place. Actually, I realize there might also be an issue in `sessions.py` line ~313 and ~242 where `.upper()` is called on method before passing to Request/PreparedRequest. But the ultimate fix in `prepare_method` would handle all paths. However, let me also check the `resolve_redirects` method in sessions.py where `method` is set directly (like `method = 'GET'`), which is already a byte string so that's fine. Let me fix `prepare_method` in models.py to ensure the method is converted to a native string.

Now I understand the issue. When a Unicode method name like `u'POST'` is passed, `method.upper()` returns a Unicode string. This Unicode value eventually reaches `httplib` where it gets concatenated with byte strings (the message body), causing Python 2 to try decoding the byte string as ASCII and failing. The fix should be in `models.py`'s `prepare_method` — the centralized place where the HTTP method is prepared. We need to ensure the method is always a native string (bytes in Python 2, str in Python 3). The `to_native_string` function already exists and is imported in `models.py` for this exact purpose.

Now let me verify the fix by looking at the modified file and running a quick test.

Let me verify the fix looks correct:

Wait, the type is `<class 'str'>`. In Python 2, the built-in `str` is the byte string type. Let me check: in `compat.py`, `str = unicode` is defined, but that only affects the `str` name within the `compat` module and wherever it's imported. Let me check what `str` is in the test script context. Actually, in the test I ran, `str` is the Python built-in `str` (byte string). The compat module redefines `str` to `unicode` but that's only when you import `str` from `.compat`. Let me verify: ```python from requests.compat import str as compat_str ``` In models.py, `str` is imported from `.compat`, so within models.py, `str` is `unicode`. But `to_native_string` should convert it to `builtin_str` (which is the native `str` in Python 2, i.e., byte string). The output shows `type(p.method)` is `<class 'str'>` which in Python 2 is the byte string. So the fix works correctly. Let me also run a more comprehensive test to verify the original bug scenario.

The method is now properly converted to a native byte string. Let me also verify the original bug scenario with a more comprehensive test:

Let me adjust the test.

The fix works. Let me also run the existing test suite to make sure nothing is broken.

Let me run the existing test suite to ensure nothing is broken:

The one failing test (`test_DIGEST_AUTH_RETURNS_COOKIE`) is unrelated to my change — it's a network-dependent test that returns 502 (likely an issue with the httpbin service). Let me run tests that are specifically related to method handling to verify my fix doesn't break anything. Let me also check if there are specific tests for unicode methods.

That test failure is unrelated to our change — it's a network-dependent test receiving a 502 from httpbin. Let me run just the unit tests to make sure nothing is broken:

Let me try a simpler test.

The fix works correctly. Let me also check that there are no other places in the codebase where a unicode method could slip through. Let me also check the `sessions.py` file more carefully - there are two places where `.upper()` is called on method, and also the `resolve_redirects` method where `method` is set to string literals like `'GET'`, `'HEAD'` (which are already native strings). Let me verify by looking at the code paths: 1. `Session.request()` line ~313: `method = method.upper()` — this creates a Request object with the uppercased method. But this is then passed to `prepare_request()` which calls `p.prepare(method=request.method.upper(), ...)`, which calls `prepare_method()` again. So even if we fix `prepare_method`, the method is still uppercased in `Session.request()`. However, since `prepare_method` will be called again in the prepare flow, the fix there should handle it. 2. `Session.prepare_request()` line ~242: `method=request.method.upper()` — same as above, this is passed to `prepare()` which calls `prepare_method()`. 3. `PreparedRequest.prepare_method()` — this is where we just applied the fix. So the fix is in the right place. Even if a unicode method enters through `Session.request()` and gets `.upper()` called there (keeping it unicode), it will be converted to native string when `prepare_method` is eventually called. But wait, let me also check whether `to_native_string` handles the case where the input is already a native string (byte string). Looking at the function: ```python def to_native_string(string, encoding='ascii'): if isinstance(string, builtin_str): out = string else: if is_py2: out = string.encode(encoding) else: out = string.decode(encoding) return out ``` In Python 2: - If `string` is already `builtin_str` (i.e., byte string), it returns as-is. - If `string` is unicode, it encodes to ASCII. HTTP methods are always ASCII, so this is fine. The fix is complete and correct.

The fix is working correctly. Let me also quickly verify there are no other places where a unicode method could bypass `prepare_method`: