gh-56915: Fix documented timeout default in ftplib and poplib

[Monstertov]

the docs show timeout=None as the default for FTP, FTP.connect, FTP_TLS and POP3_SSL, but none of them actually default to None:

• FTP, FTP_TLS and POP3_SSL default to socket._GLOBAL_DEFAULT_TIMEOUT, so the global default timeout is used. passing None explicitly disables the timeout, which is the surprise described in the issue.
• FTP.connect uses a private sentinel and keeps the timeout that was given to the constructor.

this switches those signatures to the [, timeout] form that smtplib, http.client, urllib.request and POP3 already use, fixes the default text for FTP.connect, and corrects the FTP class docstring, which said the timeout defaults to None.

docs and docstring only, no behaviour change, so i think this can skip news.

quick check of the current behaviour:

socket.setdefaulttimeout(7.0)
FTP().connect(host, port)              # sock.gettimeout() -> 7.0
FTP(timeout=None).connect(host, port)  # sock.gettimeout() -> None
FTP(timeout=3).connect(host, port)     # sock.gettimeout() -> 3.0

• Issue: timeout sentinel in ftplib and poplib documentation #56915

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #34909323 | 📁 Comparing 419c1a3 against main (1a85213)

  🔍 Preview build  

2 files changed

± library/ftplib.html
± library/poplib.html