bpo-45975: Simplify some while-loops with walrus operator (GH-29347)

Lib/_pyio.py

@@ -638,10 +638,7 @@ class RawIOBase(IOBase):
     def readall(self):
         """Read until EOF, using multiple read() call."""
         res = bytearray()
-        while True:
+        while data := self.read(DEFAULT_BUFFER_SIZE):
-            data = self.read(DEFAULT_BUFFER_SIZE)
-            if not data:
-                break
             res += data
         if res:
             return bytes(res)

Lib/base64.py

@@ -508,14 +508,8 @@ MAXBINSIZE = (MAXLINESIZE//4)*3
 
 def encode(input, output):
     """Encode a file; input and output are binary files."""
-    while True:
+    while s := input.read(MAXBINSIZE):
-        s = input.read(MAXBINSIZE)
+        while len(s) < MAXBINSIZE and (ns := input.read(MAXBINSIZE-len(s))):
-        if not s:
-            break
-        while len(s) < MAXBINSIZE:
-            ns = input.read(MAXBINSIZE-len(s))
-            if not ns:
-                break
             s += ns
         line = binascii.b2a_base64(s)
         output.write(line)
@@ -523,10 +517,7 @@ def encode(input, output):
 
 def decode(input, output):
     """Decode a file; input and output are binary files."""
-    while True:
+    while line := input.readline():
-        line = input.readline()
-        if not line:
-            break
         s = binascii.a2b_base64(line)
         output.write(s)
 

Lib/ctypes/_aix.py

@@ -108,12 +108,8 @@ def get_ld_headers(file):
     p = Popen(["/usr/bin/dump", f"-X{AIX_ABI}", "-H", file],
         universal_newlines=True, stdout=PIPE, stderr=DEVNULL)
     # be sure to read to the end-of-file - getting all entries
-    while True:
+    while ld_header := get_ld_header(p):
-        ld_header = get_ld_header(p)
+        ldr_headers.append((ld_header, get_ld_header_info(p)))
-        if ld_header:
-            ldr_headers.append((ld_header, get_ld_header_info(p)))
-        else:
-            break
     p.stdout.close()
     p.wait()
     return ldr_headers

Lib/email/parser.py

@@ -49,10 +49,7 @@ class Parser:
         feedparser = FeedParser(self._class, policy=self.policy)
         if headersonly:
             feedparser._set_headersonly()
-        while True:
+        while data := fp.read(8192):
-            data = fp.read(8192)
-            if not data:
-                break
             feedparser.feed(data)
         return feedparser.close()
 

Lib/ftplib.py

@@ -434,10 +434,7 @@ class FTP:
         """
         self.voidcmd('TYPE I')
         with self.transfercmd(cmd, rest) as conn:
-            while 1:
+            while data := conn.recv(blocksize):
-                data = conn.recv(blocksize)
-                if not data:
-                    break
                 callback(data)
             # shutdown ssl layer
             if _SSLSocket is not None and isinstance(conn, _SSLSocket):
@@ -496,10 +493,7 @@ class FTP:
         """
         self.voidcmd('TYPE I')
         with self.transfercmd(cmd, rest) as conn:
-            while 1:
+            while buf := fp.read(blocksize):
-                buf = fp.read(blocksize)
-                if not buf:
-                    break
                 conn.sendall(buf)
                 if callback:
                     callback(buf)

Lib/http/client.py

@@ -578,11 +578,7 @@ class HTTPResponse(io.BufferedIOBase):
         assert self.chunked != _UNKNOWN
         value = []
         try:
-            while True:
+            while (chunk_left := self._get_chunk_left()) is not None:
-                chunk_left = self._get_chunk_left()
-                if chunk_left is None:
-                    break
-
                 if amt is not None and amt <= chunk_left:
                     value.append(self._safe_read(amt))
                     self.chunk_left = chunk_left - amt
@@ -998,10 +994,7 @@ class HTTPConnection:
             encode = self._is_textIO(data)
             if encode and self.debuglevel > 0:
                 print("encoding file using iso-8859-1")
-            while 1:
+            while datablock := data.read(self.blocksize):
-                datablock = data.read(self.blocksize)
-                if not datablock:
-                    break
                 if encode:
                     datablock = datablock.encode("iso-8859-1")
                 sys.audit("http.client.send", self, datablock)
@@ -1031,10 +1024,7 @@ class HTTPConnection:
         encode = self._is_textIO(readable)
         if encode and self.debuglevel > 0:
             print("encoding file using iso-8859-1")
-        while True:
+        while datablock := readable.read(self.blocksize):
-            datablock = readable.read(self.blocksize)
-            if not datablock:
-                break
             if encode:
                 datablock = datablock.encode("iso-8859-1")
             yield datablock

Lib/http/cookiejar.py

@@ -1915,9 +1915,7 @@ class LWPCookieJar(FileCookieJar):
                        "comment", "commenturl")
 
         try:
-            while 1:
+            while (line := f.readline()) != "":
-                line = f.readline()
-                if line == "": break
                 if not line.startswith(header):
                     continue
                 line = line[len(header):].strip()
@@ -2017,12 +2015,9 @@ class MozillaCookieJar(FileCookieJar):
                 filename)
 
         try:
-            while 1:
+            while (line := f.readline()) != "":
-                line = f.readline()
                 rest = {}
 
-                if line == "": break
-
                 # httponly is a cookie flag as defined in rfc6265
                 # when encoded in a netscape cookie file,
                 # the line is prepended with "#HttpOnly_"

Lib/mailbox.py

@@ -1956,10 +1956,7 @@ class _ProxyFile:
 
     def __iter__(self):
         """Iterate over lines."""
-        while True:
+        while line := self.readline():
-            line = self.readline()
-            if not line:
-                return
             yield line
 
     def tell(self):

Lib/mailcap.py

@@ -90,9 +90,7 @@ def _readmailcapfile(fp, lineno):
     the viewing command is stored with the key "view".
     """
     caps = {}
-    while 1:
+    while line := fp.readline():
-        line = fp.readline()
-        if not line: break
         # Ignore comments and blank lines
         if line[0] == '#' or line.strip() == '':
             continue

Lib/mimetypes.py

@@ -217,10 +217,7 @@ class MimeTypes:
         list of standard types, else to the list of non-standard
         types.
         """
-        while 1:
+        while line := fp.readline():
-            line = fp.readline()
-            if not line:
-                break
             words = line.split()
             for i in range(len(words)):
                 if words[i][0] == '#':

Lib/pstats.py

@@ -223,8 +223,6 @@ class Stats:
             for word, tup in self.sort_arg_dict_default.items():
                 fragment = word
                 while fragment:
-                    if not fragment:
-                        break
                     if fragment in dict:
                         bad_list[fragment] = 0
                         break

Lib/pydoc.py

@@ -686,9 +686,7 @@ class HTMLDoc(Doc):
                                 r'RFC[- ]?(\d+)|'
                                 r'PEP[- ]?(\d+)|'
                                 r'(self\.)?(\w+))')
-        while True:
+        while match := pattern.search(text, here):
-            match = pattern.search(text, here)
-            if not match: break
             start, end = match.span()
             results.append(escape(text[here:start]))
 

Lib/quopri.py

@@ -67,10 +67,7 @@ def encode(input, output, quotetabs, header=False):
             output.write(s + lineEnd)
 
     prevline = None
-    while 1:
+    while line := input.readline():
-        line = input.readline()
-        if not line:
-            break
         outline = []
         # Strip off any readline induced trailing newline
         stripped = b''
@@ -126,9 +123,7 @@ def decode(input, output, header=False):
         return
 
     new = b''
-    while 1:
+    while line := input.readline():
-        line = input.readline()
-        if not line: break
         i, n = 0, len(line)
         if n > 0 and line[n-1:n] == b'\n':
             partial = 0; n = n-1

Lib/shlex.py

@@ -333,10 +333,7 @@ def quote(s):
 
 
 def _print_tokens(lexer):
-    while 1:
+    while tt := lexer.get_token():
-        tt = lexer.get_token()
-        if not tt:
-            break
         print("Token: " + repr(tt))
 
 if __name__ == '__main__':

Lib/shutil.py

@@ -194,10 +194,7 @@ def copyfileobj(fsrc, fdst, length=0):
     # Localize variable access to minimize overhead.
     fsrc_read = fsrc.read
     fdst_write = fdst.write
-    while True:
+    while buf := fsrc_read(length):
-        buf = fsrc_read(length)
-        if not buf:
-            break
         fdst_write(buf)
 
 def _samefile(src, dst):

Lib/smtplib.py

@@ -1099,10 +1099,7 @@ if __name__ == '__main__':
     toaddrs = prompt("To").split(',')
     print("Enter message, end with ^D:")
     msg = ''
-    while 1:
+    while line := sys.stdin.readline():
-        line = sys.stdin.readline()
-        if not line:
-            break
         msg = msg + line
     print("Message length is %d" % len(msg))
 

Lib/socketserver.py

@@ -292,8 +292,7 @@ class BaseServer:
             selector.register(self, selectors.EVENT_READ)
 
             while True:
-                ready = selector.select(timeout)
+                if selector.select(timeout):
-                if ready:
                     return self._handle_request_noblock()
                 else:
                     if timeout is not None:

Lib/tarfile.py

@@ -1262,11 +1262,7 @@ class TarInfo(object):
         # the newline. keyword and value are both UTF-8 encoded strings.
         regex = re.compile(br"(\d+) ([^=]+)=")
         pos = 0
-        while True:
+        while match := regex.match(buf, pos):
-            match = regex.match(buf, pos)
-            if not match:
-                break
-
             length, keyword = match.groups()
             length = int(length)
             if length == 0:
@@ -2418,10 +2414,8 @@ class TarFile(object):
         """Read through the entire archive file and look for readable
            members.
         """
-        while True:
+        while self.next() is not None:
-            tarinfo = self.next()
+            pass
-            if tarinfo is None:
-                break
         self._loaded = True
 
     def _check(self, mode=None):

Lib/test/test_lzma.py

@@ -825,10 +825,7 @@ class FileTestCase(unittest.TestCase):
     def test_read_10(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ)) as f:
             chunks = []
-            while True:
+            while result := f.read(10):
-                result = f.read(10)
-                if not result:
-                    break
                 self.assertLessEqual(len(result), 10)
                 chunks.append(result)
             self.assertEqual(b"".join(chunks), INPUT)
@@ -911,10 +908,7 @@ class FileTestCase(unittest.TestCase):
     def test_read1(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ)) as f:
             blocks = []
-            while True:
+            while result := f.read1():
-                result = f.read1()
-                if not result:
-                    break
                 blocks.append(result)
             self.assertEqual(b"".join(blocks), INPUT)
             self.assertEqual(f.read1(), b"")
@@ -926,10 +920,7 @@ class FileTestCase(unittest.TestCase):
     def test_read1_10(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ)) as f:
             blocks = []
-            while True:
+            while result := f.read1(10):
-                result = f.read1(10)
-                if not result:
-                    break
                 blocks.append(result)
             self.assertEqual(b"".join(blocks), INPUT)
             self.assertEqual(f.read1(), b"")
@@ -937,10 +928,7 @@ class FileTestCase(unittest.TestCase):
     def test_read1_multistream(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ * 5)) as f:
             blocks = []
-            while True:
+            while result := f.read1():
-                result = f.read1()
-                if not result:
-                    break
                 blocks.append(result)
             self.assertEqual(b"".join(blocks), INPUT * 5)
             self.assertEqual(f.read1(), b"")

Lib/urllib/request.py

@@ -265,10 +265,7 @@ def urlretrieve(url, filename=None, reporthook=None, data=None):
             if reporthook:
                 reporthook(blocknum, bs, size)
 
-            while True:
+            while block := fp.read(bs):
-                block = fp.read(bs)
-                if not block:
-                    break
                 read += len(block)
                 tfp.write(block)
                 blocknum += 1
@@ -1847,10 +1844,7 @@ class URLopener:
                     size = int(headers["Content-Length"])
                 if reporthook:
                     reporthook(blocknum, bs, size)
-                while 1:
+                while block := fp.read(bs):
-                    block = fp.read(bs)
-                    if not block:
-                        break
                     read += len(block)
                     tfp.write(block)
                     blocknum += 1

Lib/wsgiref/handlers.py

@@ -475,10 +475,7 @@ class SimpleHandler(BaseHandler):
         from warnings import warn
         warn("SimpleHandler.stdout.write() should not do partial writes",
             DeprecationWarning)
-        while True:
+        while data := data[result:]:
-            data = data[result:]
-            if not data:
-                break
             result = self.stdout.write(data)
 
     def _flush(self):

Lib/wsgiref/validate.py

@@ -214,10 +214,7 @@ class InputWrapper:
         return lines
 
     def __iter__(self):
-        while 1:
+        while line := self.readline():
-            line = self.readline()
-            if not line:
-                return
             yield line
 
     def close(self):

Lib/xdrlib.py

@@ -224,9 +224,7 @@ class Unpacker:
 
     def unpack_list(self, unpack_item):
         list = []
-        while 1:
+        while (x := self.unpack_uint()) != 0:
-            x = self.unpack_uint()
-            if x == 0: break
             if x != 1:
                 raise ConversionError('0 or 1 expected, got %r' % (x,))
             item = unpack_item()

Lib/xml/dom/expatbuilder.py

@@ -200,10 +200,7 @@ class ExpatBuilder:
         parser = self.getParser()
         first_buffer = True
         try:
-            while 1:
+            while buffer := file.read(16*1024):
-                buffer = file.read(16*1024)
-                if not buffer:
-                    break
                 parser.Parse(buffer, False)
                 if first_buffer and self.document.documentElement:
                     self._setup_subset(buffer)

Lib/xml/etree/ElementTree.py

@@ -566,10 +566,7 @@ class ElementTree:
                     # it with chunks.
                     self._root = parser._parse_whole(source)
                     return self._root
-            while True:
+            while data := source.read(65536):
-                data = source.read(65536)
-                if not data:
-                    break
                 parser.feed(data)
             self._root = parser.close()
             return self._root

Lib/xml/sax/xmlreader.py

@@ -120,10 +120,8 @@ class IncrementalParser(XMLReader):
         file = source.getCharacterStream()
         if file is None:
             file = source.getByteStream()
-        buffer = file.read(self._bufsize)
+        while buffer := file.read(self._bufsize):
-        while buffer:
             self.feed(buffer)
-            buffer = file.read(self._bufsize)
         self.close()
 
     def feed(self, data):

Lib/xmlrpc/client.py

@@ -1339,10 +1339,7 @@ class Transport:
 
         p, u = self.getparser()
 
-        while 1:
+        while data := stream.read(1024):
-            data = stream.read(1024)
-            if not data:
-                break
             if self.verbose:
                 print("body:", repr(data))
             p.feed(data)

Lib/xmlrpc/server.py

@@ -720,9 +720,7 @@ class ServerHTMLDoc(pydoc.HTMLDoc):
                                 r'RFC[- ]?(\d+)|'
                                 r'PEP[- ]?(\d+)|'
                                 r'(self\.)?((?:\w|\.)+))\b')
-        while 1:
+        while match := pattern.search(text, here):
-            match = pattern.search(text, here)
-            if not match: break
             start, end = match.span()
             results.append(escape(text[here:start]))