What causes "module {__name__!r} has no attribute {name!r}" in sgl-project/sglang?

sgl-project/sglang · error · AttributeError

module {name!r} has no attribute {name!r}

Error message

module {__name__!r} has no attribute {name!r}

What it means

This module uses a lazy attribute hook: only FlashAttentionForwardSm90 is importable on demand; any other attribute access on the module raises AttributeError. This avoids importing the heavy Sm90 kernel (and its CUTLASS DSL compilation machinery) unless actually needed.

Source

Thrown at python/sglang/kernels/ops/attention/flash_attn/cute/flash_fwd.py:1538

            self.score_vec_size,
            self.qk_acc_dtype,
            aux_data,
            fastdiv_mods,
            seqlen_info=seqlen,
            constant_q_idx=None,
            qhead_per_kvhead=self.qhead_per_kvhead if const_expr(self.pack_gqa) else 1,
        )


# SM90 forward pass moved to flash_fwd_sm90.py; re-export for backward compatibility
def __getattr__(name):
    if name == "FlashAttentionForwardSm90":
        from sglang.kernels.ops.attention.flash_attn.cute.flash_fwd_sm90 import (
            FlashAttentionForwardSm90,
        )

        return FlashAttentionForwardSm90
    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

View on GitHub (pinned to 0132848349)

Solutions

Import the correct symbol: from sglang.kernels.ops.attention.flash_attn.cute.flash_fwd_sm90 import FlashAttentionForwardSm90, or getattr(module, 'FlashAttentionForwardSm90')
Find the new home of the moved symbol with grep in python/sglang/kernels/ops/attention/flash_attn/cute/
Update mock.patch targets to the defining module, not this lazy facade

Example fix

// before
from sglang.kernels.ops.attention.flash_attn.cute.flash_fwd import FlashAttentionForward
// after
from sglang.kernels.ops.attention.flash_attn.cute.flash_fwd import FlashAttentionForwardSm90

Defensive patterns

Strategy: try-catch

Validate before calling

ALLOWED = ('FlashAttentionForwardSm90',)
if name not in ALLOWED:
    raise ImportError(f'{name} is not exported by flash_fwd; allowed: {ALLOWED}')

Type guard

def has_attr(mod, name) -> bool:
    return name == 'FlashAttentionForwardSm90'

Try / catch

try:
    cls = getattr(flash_fwd_module, name)
except AttributeError:
    raise ImportError(f'{name} moved; import from flash_fwd_sm90 directly') from None

Prevention

Import symbols from their defining module (flash_fwd_sm90), not the lazy facade
After file splits, grep for old import paths before assuming they work
Pin mock.patch targets to defining modules

When it happens

Trigger: Doing from ...flash_fwd import FlashAttentionForward or accessing any name other than FlashAttentionForwardSm90 on the module, e.g. via importlib, getattr(module, name), or tab-completion-driven code. Also triggered by tools like mock.patch('...flash_fwd.Something') or hasattr probes.

Common situations: Refactoring imports after a file split where older names lived in this module; test frameworks patching module attributes; static-analysis or dynamic-import code enumerating module members.

Related errors

AI-assisted analysis of sgl-project/sglang@0132848349 (2026-08-28). Data as JSON: /api/errors/dd5be80236f24cbf. Report an issue: GitHub.