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

Author: nickdrozd

Diff for: Lib/_pyio.py

@@ -638,10 +638,7 @@ def read(self, size=-1):
     def readall(self):
         """Read until EOF, using multiple read() call."""
         res = bytearray()
-        while True:
-            data = self.read(DEFAULT_BUFFER_SIZE)
-            if not data:
-                break
+        while data := self.read(DEFAULT_BUFFER_SIZE):
             res += data
         if res:
             return bytes(res)

Diff for: Lib/base64.py

@@ -508,25 +508,16 @@ def b85decode(b):
 
 def encode(input, output):
     """Encode a file; input and output are binary files."""
-    while True:
-        s = input.read(MAXBINSIZE)
-        if not s:
-            break
-        while len(s) < MAXBINSIZE:
-            ns = input.read(MAXBINSIZE-len(s))
-            if not ns:
-                break
+    while s := input.read(MAXBINSIZE):
+        while len(s) < MAXBINSIZE and (ns := input.read(MAXBINSIZE-len(s))):
             s += ns
         line = binascii.b2a_base64(s)
         output.write(line)
 
 
 def decode(input, output):
     """Decode a file; input and output are binary files."""
-    while True:
-        line = input.readline()
-        if not line:
-            break
+    while line := input.readline():
         s = binascii.a2b_base64(line)
         output.write(s)
 

Diff for: 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:
-        ld_header = get_ld_header(p)
-        if ld_header:
-            ldr_headers.append((ld_header, get_ld_header_info(p)))
-        else:
-            break
+    while ld_header := get_ld_header(p):
+        ldr_headers.append((ld_header, get_ld_header_info(p)))
     p.stdout.close()
     p.wait()
     return ldr_headers

Diff for: Lib/email/parser.py

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

Diff for: Lib/ftplib.py

@@ -434,10 +434,7 @@ def retrbinary(self, cmd, callback, blocksize=8192, rest=None):
         """
         self.voidcmd('TYPE I')
         with self.transfercmd(cmd, rest) as conn:
-            while 1:
-                data = conn.recv(blocksize)
-                if not data:
-                    break
+            while data := conn.recv(blocksize):
                 callback(data)
             # shutdown ssl layer
             if _SSLSocket is not None and isinstance(conn, _SSLSocket):
@@ -496,10 +493,7 @@ def storbinary(self, cmd, fp, blocksize=8192, callback=None, rest=None):
         """
         self.voidcmd('TYPE I')
         with self.transfercmd(cmd, rest) as conn:
-            while 1:
-                buf = fp.read(blocksize)
-                if not buf:
-                    break
+            while buf := fp.read(blocksize):
                 conn.sendall(buf)
                 if callback:
                     callback(buf)

Diff for: Lib/http/client.py

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

Diff for: Lib/http/cookiejar.py

@@ -1915,9 +1915,7 @@ def _really_load(self, f, filename, ignore_discard, ignore_expires):
                        "comment", "commenturl")
 
         try:
-            while 1:
-                line = f.readline()
-                if line == "": break
+            while (line := f.readline()) != "":
                 if not line.startswith(header):
                     continue
                 line = line[len(header):].strip()
@@ -2017,12 +2015,9 @@ def _really_load(self, f, filename, ignore_discard, ignore_expires):
                 filename)
 
         try:
-            while 1:
-                line = f.readline()
+            while (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_"

Diff for: Lib/mailbox.py

@@ -1956,10 +1956,7 @@ def readlines(self, sizehint=None):
 
     def __iter__(self):
         """Iterate over lines."""
-        while True:
-            line = self.readline()
-            if not line:
-                return
+        while line := self.readline():
             yield line
 
     def tell(self):

Diff for: Lib/mailcap.py

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

Diff for: Lib/mimetypes.py

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

Diff for: Lib/pstats.py

@@ -223,8 +223,6 @@ def get_sort_arg_defs(self):
             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

Diff for: Lib/pydoc.py

@@ -686,9 +686,7 @@ def markup(self, text, escape=None, funcs={}, classes={}, methods={}):
                                 r'RFC[- ]?(\d+)|'
                                 r'PEP[- ]?(\d+)|'
                                 r'(self\.)?(\w+))')
-        while True:
-            match = pattern.search(text, here)
-            if not match: break
+        while match := pattern.search(text, here):
             start, end = match.span()
             results.append(escape(text[here:start]))
 

Diff for: Lib/quopri.py

@@ -67,10 +67,7 @@ def write(s, output=output, lineEnd=b'\n'):
             output.write(s + lineEnd)
 
     prevline = None
-    while 1:
-        line = input.readline()
-        if not line:
-            break
+    while line := input.readline():
         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:
-        line = input.readline()
-        if not line: break
+    while line := input.readline():
         i, n = 0, len(line)
         if n > 0 and line[n-1:n] == b'\n':
             partial = 0; n = n-1

Diff for: Lib/shlex.py

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

Diff for: 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:
-        buf = fsrc_read(length)
-        if not buf:
-            break
+    while buf := fsrc_read(length):
         fdst_write(buf)
 
 def _samefile(src, dst):

Diff for: Lib/smtplib.py

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

Diff for: Lib/socketserver.py

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

Diff for: Lib/tarfile.py

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

Diff for: Lib/test/test_lzma.py

@@ -825,10 +825,7 @@ def test_read_0(self):
     def test_read_10(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ)) as f:
             chunks = []
-            while True:
-                result = f.read(10)
-                if not result:
-                    break
+            while result := f.read(10):
                 self.assertLessEqual(len(result), 10)
                 chunks.append(result)
             self.assertEqual(b"".join(chunks), INPUT)
@@ -911,10 +908,7 @@ def test_read_bad_data(self):
     def test_read1(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ)) as f:
             blocks = []
-            while True:
-                result = f.read1()
-                if not result:
-                    break
+            while result := f.read1():
                 blocks.append(result)
             self.assertEqual(b"".join(blocks), INPUT)
             self.assertEqual(f.read1(), b"")
@@ -926,21 +920,15 @@ def test_read1_0(self):
     def test_read1_10(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ)) as f:
             blocks = []
-            while True:
-                result = f.read1(10)
-                if not result:
-                    break
+            while result := f.read1(10):
                 blocks.append(result)
             self.assertEqual(b"".join(blocks), INPUT)
             self.assertEqual(f.read1(), b"")
 
     def test_read1_multistream(self):
         with LZMAFile(BytesIO(COMPRESSED_XZ * 5)) as f:
             blocks = []
-            while True:
-                result = f.read1()
-                if not result:
-                    break
+            while result := f.read1():
                 blocks.append(result)
             self.assertEqual(b"".join(blocks), INPUT * 5)
             self.assertEqual(f.read1(), b"")

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

Diff for: Lib/wsgiref/handlers.py

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

Diff for: Lib/wsgiref/validate.py

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