Prevent --browser from opening when no report is generated · Issue #145306 · python/cpython · GitHub

Bug report

Bug description:

When profiling a script that does not produce HTML output, the following warning is displayed:
Warning: No functions found in profiling data. Check if sampling captured any data.
However, when the --browser option is specified, the program still attempts to open the output file in a browser.

./python -m profiling.sampling run --flamegraph --browser script.py

# script.py
print("hello world")

Suggested Fix

diff --git a/Lib/profiling/sampling/cli.py b/Lib/profiling/sampling/cli.py
index f4b31aad45b..75a21429705 100644
--- a/Lib/profiling/sampling/cli.py
+++ b/Lib/profiling/sampling/cli.py
@@ -607,6 +607,10 @@ def _open_in_browser(path):
     """
     abs_path = os.path.abspath(path)
 
+    if not os.path.exists(abs_path):
+        print(f"Warning: Could not find {abs_path}", file=sys.stderr)
+        return
+
     # For heatmap directories, open the index.html file
     if os.path.isdir(abs_path):
         index_path = os.path.join(abs_path, 'index.html')

I can open a PR with a proposed fix

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

Thanks for the report, something like this sound sensible.

We already get a warning:

hello world
Captured 1 samples in 0.00 seconds
Sample rate: 877.29 samples/sec
Error rate: 100.00
Flamegraph data: 0 root functions, total samples: 0, 1 unique strings
Warning: No functions found in profiling data. Check if sampling captured any data.

Rather than checking if the file exists and printing another warning, perhaps we could have export return a success/fail code?

cpython/Lib/profiling/sampling/cli.py

Lines 663 to 667 in 11eec7a

    
           collector.export(filename) 
        
           # Auto-open browser for HTML output if --browser flag is set 
        
           if args.format in ('flamegraph', 'heatmap') and getattr(args, 'browser', False): 
        
               _open_in_browser(filename)

cpython/Lib/profiling/sampling/cli.py

Lines 1206 to 1210 in 11eec7a

    
           collector.export(filename) 
        
           # Auto-open browser for HTML output if --browser flag is set 
        
           if args.format in ('flamegraph', 'heatmap') and getattr(args, 'browser', False): 
        
               _open_in_browser(filename)

Here's one of them, we'd have to check if it makes sense for the others:

cpython/Lib/profiling/sampling/stack_collector.py

Lines 152 to 156 in 11eec7a

    
           if num_functions == 0: 
        
               print( 
        
                   "Warning: No functions found in profiling data. Check if sampling captured any data." 
        
               ) 
        
               return

cc @pablogsal

pythongh-145306: gate --browser on export success

pythongh-145306: keep a single regression test

Merge branch 'main' into pythongh-145306-browser-export-success

Yes I agree with this approach. Printing another warning feels redundant here.

gh-145306: Fix browser open after empty export (#150017)

[3.15] gh-145306: Fix browser open after empty export (GH-150017) (#1…

Prevent --browser from opening when no report is generated · Issue #145306 · python/cpython · GitHub

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Prevent --browser from opening when no report is generated #145306

Bug report

Bug description:

Suggested Fix

CPython versions tested on:

Operating systems tested on:

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	collector.export(filename)

	# Auto-open browser for HTML output if --browser flag is set
	if args.format in ('flamegraph', 'heatmap') and getattr(args, 'browser', False):
	_open_in_browser(filename)

	if num_functions == 0:
	print(
	"Warning: No functions found in profiling data. Check if sampling captured any data."
	)
	return

Prevent --browser from opening when no report is generated · Issue #145306 · python/cpython · GitHub

Repository navigation

Prevent --browser from opening when no report is generated #145306

Description

Bug report

Bug description:

Suggested Fix

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

hugovk commented on Feb 27, 2026

misa-j commented on Feb 28, 2026

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