pdb: modernize find_function() and add tests for it.

Closes #18714.

1 files changed, 5 insertions, 12 deletions

diff --git a/Lib/pdb.py b/Lib/pdb.py
index 1ec83da..143b925 100755
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -95,18 +95,11 @@ def find_function(funcname, filename):
     except OSError:
         return None
     # consumer of this info expects the first line to be 1
-    lineno = 1
-    answer = None
-    while True:
-        line = fp.readline()
-        if line == '':
-            break
-        if cre.match(line):
-            answer = funcname, filename, lineno
-            break
-        lineno += 1
-    fp.close()
-    return answer
+    with fp:
+        for lineno, line in enumerate(fp, start=1):
+            if cre.match(line):
+                return funcname, filename, lineno
+    return None
 
 def getsourcelines(obj):
     lines, lineno = inspect.findsource(obj)