--- title: Python 3.15's best new features | daily.dev description: Python 3.15 ships with UTF-8 as the default file encoding on all operating systems (including Windows, which previously used legacy code pages like CP-1252), a... canonical: https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Python 3.15's best new features | daily.dev og:description: Python 3.15 ships with UTF-8 as the default file encoding on all operating systems (including Windows, which previously used legacy code pages like CP-1252), a... og:url: https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2 og:image: https://api.daily.dev/og/posts/nuzdgpEF2.png og:image:alt: Python 3.15's best new features og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Python 3.15's best new features **[Planet Python](https://daily.dev/sources/planetpython)** · 10 min read · 1 upvotes · 0 comments ## Summary Python 3.15 ships with UTF-8 as the default file encoding on all operating systems (including Windows, which previously used legacy code pages like CP-1252), a new built-in sentinel type for creating named sentinel values, iterable/dict unpacking support inside comprehensions (e.g. [*sub for sub in nested]), explicit lazy imports via the lazy keyword for faster startup, and a new profiling package with a low-overhead sampling profiler (profiling.sampling) that can attach to already-running processes. Other additions include improved error messages suggesting correct method names, more colorized CLI output, a new frozendict type, pprint's expand=True option, and re.prefixmatch as a clearer alias for re.match. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is the default file encoding in Python 3.15 on Windows? Python 3.15 makes UTF-8 the default file encoding on all operating systems, including Windows. Previously Windows used a legacy code page such as CP-1252 depending on system language settings, which could silently garble accented characters or raise a UnicodeEncodeError when writing emoji. Now a file written on one machine reads correctly on every other machine without passing encoding explicitly. _Teams shipping cross-platform Python tools can track encoding changes like this one on daily.dev before they hit production._ ### How do explicit lazy imports work in Python 3.15? Python 3.15 adds a lazy keyword, used as 'lazy import json' or 'lazy from collections import Counter', which defers loading a module until it's first actually used rather than at import time. This is primarily meant to improve startup time in command-line programs where some modules may never execute, and provides little benefit in long-running processes like web servers. _Developers optimizing CLI startup times can follow syntax changes like lazy imports on daily.dev._ ### Can you use asterisk unpacking inside a list comprehension in Python? As of Python 3.15, yes: syntax like [*sub for sub in nested] now flattens a list of lists directly inside a comprehension, whereas Python 3.14 and earlier raised a SyntaxError and required a double for-clause comprehension such as [x for sub in nested for x in sub]. This also works in set comprehensions, generator expressions, and dict comprehensions using double asterisk unpacking. _Python developers adopting new syntax features can keep up with changes like comprehension unpacking on daily.dev._ ## Similar posts on daily.dev - [Python Insider: Python 3.15.0 alpha 6](https://daily.dev/posts/python-insider-python-3-15-0-alpha-6-f85iqcqtk) · Python Insider · 10 upvotes · 0 comments - [Exciting Python features are on the way](https://daily.dev/posts/exciting-python-features-are-on-the-way-u7lhkabec) · InfoWorld · 0 upvotes · 0 comments --- Tags: [#python](https://daily.dev/tags/python) [View this post on daily.dev](https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Python 3.15's best new features","url":"https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2"},"datePublished":"2026-10-09T16:52:27.577Z","dateModified":"2026-10-12T09:56:58.335Z","description":"Python 3.15 ships with UTF-8 as the default file encoding on all operating systems (including Windows, which previously used legacy code pages like CP-1252), a...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/1fd94a366083de5a1b171157110815cf?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/1fd94a366083de5a1b171157110815cf?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Planet Python","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Planet Python","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/eac3cc584cb043b5a242d13752bd3d0c","url":"https://daily.dev/sources/planetpython"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"python","timeRequired":"PT10M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Planet Python","item":"https://daily.dev/sources/planetpython"},{"@type":"ListItem","position":3,"name":"Python 3.15's best new features"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/python-3-15-s-best-new-features-nuzdgpef2#faq","mainEntity":[{"@type":"Question","name":"What is the default file encoding in Python 3.15 on Windows?","acceptedAnswer":{"@type":"Answer","text":"Python 3.15 makes UTF-8 the default file encoding on all operating systems, including Windows. 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