Windows regression in Prefect 3.4.19: prefect deploy wizard skips flow discovery (“Scanning for flows…”) compared to 3.3.6

[zzstoatzz]

This discussion was created from a Slack thread conversation.

Original Thread: https://prefect-community.slack.com/archives/C04DZJC94DC/p1758656241255729

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Summary
On Windows with Python 3.12.8, the interactive prefect deploy wizard in Prefect 3.4.19 appears to skip the flow discovery step entirely and proceeds directly to the work pool selection after choosing “No, configure a new deployment”. Regressing to 3.3.6 restores the expected behavior where the wizard prints “Scanning for flows…” and lists discovered flows before prompting for the work pool.

Environment (failing)

• OS: Windows (win32/AMD64)
• Python: 3.12.8
• Prefect: 3.4.19
• API version: 0.8.4
• Pydantic: 2.11.9
• Integrations installed: prefect-aws 0.5.13, prefect-dbt 0.7.8, prefect-email 0.4.2, prefect-redis 0.2.5, prefect-shell 0.3.1
• Profile: cloud-dev (Prefect Cloud)

Environment (working)

• Same OS/Python
• Prefect: 3.3.6
• API version: 0.8.4
• Integrations: similar set

Behavior difference

• 3.3.6: After selecting “No, configure a new deployment”, the wizard prints “Scanning for flows…” and shows a list of discovered flows and their files. It also prints SyntaxWarnings about invalid escape sequences (e.g., \d, \-) during the scan. The warnings show as <unknown>:line: SyntaxWarning: invalid escape sequence … (no file path).
• 3.4.19: After selecting “No, configure a new deployment”, there is no “Scanning for flows…” output, and no flow list is shown. The wizard jumps straight to “Which work pool would you like to deploy this flow to?”. No SyntaxWarnings are printed either. This suggests the scan is not running or is failing silently.

Direct entrypoint deploy works in both versions

• prefect deploy engineering\tools\get_ip.py:get_ip -n debug_direct succeeds, indicating imports and API connectivity are fine in the failing environment and that the issue is specific to the discovery step of the wizard.

prefect.yaml from the project (redacted)

name: prefect-scripts
prefect-version: v3.4.19

pull:
- prefect.deployments.steps.git_clone:
    repository: https://github.com/<redacted>/prefect-scripts.git
    branch: master
    credentials: '{{ prefect.blocks.github-credentials.<redacted> }}'

deployments:
  - name: dbt_run_sprout_social
    description: "trigger Sprout Social dbt job - https://cloud.getdbt.com/deploy/<redacted>/projects/<redacted>/jobs/873616"
    entrypoint: engineering\tools\run_dbt_job.py:run_dbt_job_flow
    parameters: {"dbt_cloud_job_identifier": "sprout-social-dbt"}
  - name: dbt_run_bitly_digital
    description: "trigger Bitly Digital dbt job - https://cloud.getdbt.com/deploy/<redacted>/projects/<redacted>/jobs/911051"
    entrypoint: engineering\tools\run_dbt_job.py:run_dbt_job_flow
    parameters: {"dbt_cloud_job_identifier": "bitly-digital-dbt"}

Additional notes

• .prefectignore does not appear to influence the interactive discovery step; ignored directories still appear in 3.3.6’s scan list. It does affect packaging/upload, but discovery still traverses files.
• In 3.3.6, SyntaxWarnings printed during scan are reported as <unknown> instead of including the offending file path, which makes remediation harder. The user can reproduce and remove those warnings by compiling with python -W default -m py_compile or python -W default -X dev -m compileall -q ..
• With 3.4.19, no warnings and no discovery output are shown at all; the first prompt after “No, configure a new deployment” is the work pool selection.

Repro steps

1. On Windows with Python 3.12.8, in a repo containing multiple flows (some with backslash-containing strings that may trigger invalid escape sequence warnings), run prefect deploy.
2. At the prompt “Would you like to use an existing deployment configuration?”, select “No, configure a new deployment”.
3. Observe: on 3.3.6, you’ll see “Scanning for flows…” then a list of flows; on 3.4.19, you’ll be prompted for work pool immediately with no scan output.
4. As a control, run prefect deploy path\to\file.py:flow_name -n test — this succeeds on both versions.

Expectation

• The wizard should consistently perform and display flow discovery prior to the work pool selection, or clearly indicate if discovery failed with actionable errors.

Impact

• Users on Windows cannot use the discovery step in 3.4.x and must specify explicit entrypoints. It also hides SyntaxWarnings that were visible in 3.3.6, which could help identify problematic files.

Workarounds

• Use explicit entrypoints for deployments (works reliably): prefect deploy path\to\file.py:flow_name -n my-deploy.
• Or deploy from code using flow.from_source(...).deploy(...).
• Pin to 3.3.6 if the wizard’s discovery UX is required.

Request

• Please confirm whether this is a regression in the deploy wizard on Windows in 3.4.x. If so, guidance on a fix or a version where it’s addressed would be appreciated. Including filenames in SyntaxWarning output during discovery would also improve troubleshooting.

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This discussion was automatically created by the Marvin bot to preserve valuable community insights.

[techxorcist]

One additional note as the person whose Marvin chat led to this: The deploy wizard works under 3.4.19 if I put a prefect.yaml in a subfolder with only a few flows, none of which generate the syntax warning, so it is only this edge case where there is a syntax issue that seems related to the behavior, which is puzzling mostly because it happens without any warning or error messages.