--- title: 7 Mistakes That Are Quietly Slowing Down Your Python... description: A guide for Python beginners covering seven common mistakes that slow down learning: trying to learn too many things at once, passive watching instead of... canonical: https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: 7 Mistakes That Are Quietly Slowing Down Your Python Journey (And How to Fix Them) | daily.dev og:description: A guide for Python beginners covering seven common mistakes that slow down learning: trying to learn too many things at once, passive watching instead of... og:url: https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy og:image: https://api.daily.dev/og/posts/ZnLBpidSY.png og:image:alt: 7 Mistakes That Are Quietly Slowing Down Your Python Journey (And How to Fix Them) 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. # 7 Mistakes That Are Quietly Slowing Down Your Python Journey (And How to Fix Them) **[Medium](https://daily.dev/sources/medium_js)** · 5 min read · 0 upvotes · 0 comments ## Summary A guide for Python beginners covering seven common mistakes that slow down learning: trying to learn too many things at once, passive watching instead of active coding, mixing tabs and spaces causing IndentationError, confusing '==' with 'is', using mutable default arguments, fearing error messages, and using unclear variable names. Each mistake includes a concrete fix with code examples. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why does using a mutable default argument like an empty list in a Python function cause unexpected behavior? A mutable default argument such as an empty list is created only once when the function is defined, not each time it is called, so it silently persists state across calls. For example, calling add_item(item, items=[]) repeatedly appends to the same list instead of starting fresh. The fix is to use items=None as the default and initialize the list inside the function body when items is None. _daily.dev surfaces practical fixes like this for developers debugging tricky Python function behavior._ ### What is the difference between using '==' and 'is' to compare two lists in Python? Using '==' compares values, while 'is' compares object identity in memory. Two lists with identical contents, such as a = [1,2,3] and b = [1,2,3], will return True for a == b but False for a is b because they are different objects. The 'is' operator should mainly be reserved for checking whether something is exactly None. _Developers sorting out subtle Python comparison bugs can find clear explanations like this on daily.dev._ ## Similar posts on daily.dev - [7 Mistakes Beginners Make When Learning Programming](https://daily.dev/posts/7-mistakes-beginners-make-when-learning-programming-oqm5ywthk) · Medium · 0 upvotes · 0 comments - [11 Beginner Tips for Learning Python Programming – Real Python](https://daily.dev/posts/11-beginner-tips-for-learning-python-programming-real-python-3k7sph5vu) · Real Python · 3 upvotes · 0 comments --- Tags: [#python](https://daily.dev/tags/python) [View this post on daily.dev](https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy) ```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":"7 Mistakes That Are Quietly Slowing Down Your Python Journey (And How to Fix Them)","url":"https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy"},"datePublished":"2026-07-26T22:00:29.785Z","dateModified":"2026-09-13T20:42:34.216Z","description":"A guide for Python beginners covering seven common mistakes that slow down learning: trying to learn too many things at once, passive watching instead of...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/ed107d2fb428c93a6c2897509c25394f?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/ed107d2fb428c93a6c2897509c25394f?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Medium","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":"Medium","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/medium","url":"https://daily.dev/sources/medium_js"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"python","timeRequired":"PT5M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Medium","item":"https://daily.dev/sources/medium_js"},{"@type":"ListItem","position":3,"name":"7 Mistakes That Are Quietly Slowing Down Your Python Journey (And How to Fix Them)"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/7-mistakes-that-are-quietly-slowing-down-your-python-journey-and-how-to-fix-them--znlbpidsy#faq","mainEntity":[{"@type":"Question","name":"Why does using a mutable default argument like an empty list in a Python function cause unexpected behavior?","acceptedAnswer":{"@type":"Answer","text":"A mutable default argument such as an empty list is created only once when the function is defined, not each time it is called, so it silently persists state across calls. 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