--- title: How Germany’s Line Ended Up on France’s Chart | daily.dev description: A debugging story about a subtle concurrency bug in matplotlib caused by its hidden global 'current figure' state. When multiple workers generated charts in... canonical: https://daily.dev/posts/how-germany-s-line-ended-up-on-france-s-chart-w6r1bwzlj twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How Germany’s Line Ended Up on France’s Chart | daily.dev og:description: A debugging story about a subtle concurrency bug in matplotlib caused by its hidden global 'current figure' state. When multiple workers generated charts in... og:url: https://daily.dev/posts/how-germany-s-line-ended-up-on-france-s-chart-w6r1bwzlj og:image: https://api.daily.dev/og/posts/W6R1Bwzlj.png og:image:alt: How Germany’s Line Ended Up on France’s Chart 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. # How Germany’s Line Ended Up on France’s Chart **[Medium](https://daily.dev/sources/medium_js)** · 6 min read · 0 upvotes · 0 comments ## Summary A debugging story about a subtle concurrency bug in matplotlib caused by its hidden global 'current figure' state. When multiple workers generated charts in parallel using the familiar plt.* shortcut API, they all wrote to the same shared figure object, causing data from one chart to appear on another — with no error raised. A secondary symptom was a slow memory leak from unclosed figures. The fix is to use matplotlib's object-oriented API (Figure and Axes objects) so each worker owns its own isolated figure. The broader lesson: convenient 'magic' APIs often hide shared global state that becomes a race condition under parallelism. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [I Made the Same Dataset Talk Five Different Ways](https://daily.dev/posts/i-made-the-same-dataset-talk-five-different-ways-x8gktpeif) · Medium · 0 upvotes · 0 comments - [Matplotlib vs Plotly: Which Python Chart Tool Should You Choose?](https://daily.dev/posts/matplotlib-vs-plotly-which-python-chart-tool-should-you-choose--i4h1lfpfx) · Towards Data Science · 1 upvotes · 0 comments - [The Matplotlib & Seaborn Functions You Actually Use in Production](https://daily.dev/posts/the-matplotlib-seaborn-functions-you-actually-use-in-production-xtmhjfxtz) · Medium · 0 upvotes · 0 comments --- Tags: [#python](https://daily.dev/tags/python), [#matplotlib](https://daily.dev/tags/matplotlib) [View this post on daily.dev](https://daily.dev/posts/how-germany-s-line-ended-up-on-france-s-chart-w6r1bwzlj) ```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":"How Germany’s Line Ended Up on France’s Chart","url":"https://daily.dev/posts/how-germany-s-line-ended-up-on-france-s-chart-w6r1bwzlj","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/how-germany-s-line-ended-up-on-france-s-chart-w6r1bwzlj"},"datePublished":"2026-07-24T01:12:03.843Z","dateModified":"2026-07-24T01:14:33.609Z","description":"A debugging story about a subtle concurrency bug in matplotlib caused by its hidden global 'current figure' state. 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