[Repo Assist] fix: replace bare except clauses with specific NetworkX exceptions

[github-actions]

🤖 This is an automated pull request from Repo Assist.

Summary

Two bare except: clauses in the dowhy codebase were masking all exceptions — including MemoryError, KeyboardInterrupt, and genuine programming bugs. This PR replaces them with the precise NetworkX exceptions that are actually expected.

Changes

dowhy/utils/graph_operations.py (line 244)

Before:

try:
    path = shortest_path(u, pa, i)
    return pa
except:
    pass

After:

try:
    path = shortest_path(u, pa, i)
    return pa
except nx.NetworkXNoPath:
    pass

networkx.algorithms.shortest_paths.generic.shortest_path raises nx.NetworkXNoPath when no path exists between pa and i. This is the only expected "not found" scenario here. This fix is consistent with the identical pattern already used in dowhy/utils/networkx_plotting.py.

dowhy/causal_identifier/id_identifier.py (line 128)

Before:

try:
    tsort_node_names = OrderedSet(list(nx.topological_sort(graph)))
except:
    raise Exception("The graph must be a directed acyclic graph (DAG).")

After:

try:
    tsort_node_names = OrderedSet(list(nx.topological_sort(graph)))
except nx.NetworkXUnfeasible:
    raise Exception("The graph must be a directed acyclic graph (DAG).")

nx.topological_sort() raises nx.NetworkXUnfeasible when the graph contains a cycle (i.e., is not a DAG). That is precisely the condition the error message describes.

Rationale

Bare except: clauses:

1. Silently swallow KeyboardInterrupt and SystemExit, making it impossible to interrupt the program
2. Hide genuine bugs (e.g. a NameError inside shortest_path would be silently ignored)
3. Are flagged by flake8 (E722) and considered an anti-pattern in Python

Both replacements are behaviour-preserving — the original intent is captured precisely by the specific exception types.

Test Status

⚠️ No Python environment with project dependencies was available in the runner for this run. The changes are pure exception-type refinements with no logic changes, and the fix in graph_operations.py mirrors the existing except nx.NetworkXNoPath: pattern already used in networkx_plotting.py. Tests will run via CI.

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