wb_download.py: use HTTPS, add a timeout and raise_for_status()

lectures/_static/lecture_specific/pandas/wb_download.py fetches the World Bank indicator over plain HTTP and writes the response body to disk without checking whether the request succeeded. Raised by Copilot while reviewing the downstream port at QuantEcon/lecture-python-programming.ml#6; it is upstream code, so it belongs here rather than in a translation edition.

Current lines 6-9:

wb_data_query = "http://api.worldbank.org/v2/en/indicator/gc.dod.totl.gd.zs?downloadformat=excel"
r = requests.get(wb_data_query)
with open('gd.xls', 'wb') as output:
    output.write(r.content)

Three points, in rough order of how much they matter:

No error check. On any non-200 response the error page body is written to gd.xls, and the failure only surfaces further down as an opaque pd.read_excel parse error rather than as the network problem it actually is. r.raise_for_status() turns that into a clear failure at the point of the fault.

Plain HTTP. api.worldbank.org serves HTTPS, so this is a free upgrade — and it is a file the lectures hold up as example code, which is the argument for getting it right beyond the MITM exposure itself.

No timeout. requests.get without timeout blocks indefinitely if the endpoint stops responding, which is an unpleasant failure mode inside a notebook build.

Suggested:

wb_data_query = "https://api.worldbank.org/v2/en/indicator/gc.dod.totl.gd.zs?downloadformat=excel"
r = requests.get(wb_data_query, timeout=30)
r.raise_for_status()
with open('gd.xls', 'wb') as output:
    output.write(r.content)

Note this script is a static asset rather than an executed cell, so nothing in CI exercises it — worth a manual check that the HTTPS endpoint returns the same workbook before merging.

開啟 lectures/_static/lecture_specific/pandas/wb_download.py，檢查第 6-9 行的 fetch。按照描述更新請求，然後手動檢查 HTTPS World Bank 端點是否回傳預期的活頁簿，因為 CI 不會執行這個靜態資產。完成的標準是失敗能夠清楚地顯現，且活頁簿仍支援下游讀取。