Attribute of type A | B | None becomes object after narrowing checks #12009

Closed
Closed
Attribute of type A | B | None becomes object after narrowing checks#12009
Labels
bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions

Description

@bluetech
bluetech
opened on Jan 18, 2022

Bug Report

When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.

To Reproduce

The following is the most minimal reproduction I was able to create.

classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)

Expected Behavior

Revealed type is A | B | None.

Actual Behavior

Revealed type is object.

I made some additional tests:

  • pyright gives A | B | None (good).
  • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
  • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
  • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
  • Changing the elif -> if gives A | B | None (good). So the elif seems essential.

Your Environment

  • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
  • Mypy command-line flags: --strict.
  • Mypy configuration options from mypy.ini (and other config files):
  • Python version used: 3.9, 3.10
  • Operating system and version: Arch Linux

Metadata

Metadata

Assignees

No one assigned

    Labels

    bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions

    Projects

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      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
       blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

      Skip to content
      Attribute of type A | B | None becomes object after narrowing checks #12009
      Closed
      Closed
      Attribute of type A | B | None becomes object after narrowing checks#12009
      Labels
      bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
      Description
      @bluetech
      bluetech
      opened on Jan 18, 2022
      Bug Report
      When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
      To Reproduce
      The following is the most minimal reproduction I was able to create.
      classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
      Expected Behavior
      Revealed type is A | B | None.
      Actual Behavior
      Revealed type is object.
      I made some additional tests:
      • pyright gives A | B | None (good).
      • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
      • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
      • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
      • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
      Your Environment
      • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
      • Mypy command-line flags: --strict.
      • Mypy configuration options from mypy.ini (and other config files):
      • Python version used: 3.9, 3.10
      • Operating system and version: Arch Linux
      Metadata
      Metadata
      Assignees
      No one assigned
        Labels
        bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

          Skip to content
          Attribute of type A | B | None becomes object after narrowing checks #12009
          Closed
          Closed
          Attribute of type A | B | None becomes object after narrowing checks#12009
          Labels
          bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
          Description
          @bluetech
          bluetech
          opened on Jan 18, 2022
          Bug Report
          When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
          To Reproduce
          The following is the most minimal reproduction I was able to create.
          classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
          Expected Behavior
          Revealed type is A | B | None.
          Actual Behavior
          Revealed type is object.
          I made some additional tests:
          • pyright gives A | B | None (good).
          • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
          • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
          • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
          • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
          Your Environment
          • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
          • Mypy command-line flags: --strict.
          • Mypy configuration options from mypy.ini (and other config files):
          • Python version used: 3.9, 3.10
          • Operating system and version: Arch Linux
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              Attribute of type A | B | None becomes object after narrowing checks #12009
              Closed
              Closed
              Attribute of type A | B | None becomes object after narrowing checks#12009
              Labels
              bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
              Description
              @bluetech
              bluetech
              opened on Jan 18, 2022
              Bug Report
              When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
              To Reproduce
              The following is the most minimal reproduction I was able to create.
              classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
              Expected Behavior
              Revealed type is A | B | None.
              Actual Behavior
              Revealed type is object.
              I made some additional tests:
              • pyright gives A | B | None (good).
              • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
              • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
              • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
              • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
              Your Environment
              • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
              • Mypy command-line flags: --strict.
              • Mypy configuration options from mypy.ini (and other config files):
              • Python version used: 3.9, 3.10
              • Operating system and version: Arch Linux
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  Attribute of type A | B | None becomes object after narrowing checks #12009
                  Closed
                  Closed
                  Attribute of type A | B | None becomes object after narrowing checks#12009
                  Labels
                  bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                  Description
                  @bluetech
                  bluetech
                  opened on Jan 18, 2022
                  Bug Report
                  When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
                  To Reproduce
                  The following is the most minimal reproduction I was able to create.
                  classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
                  Expected Behavior
                  Revealed type is A | B | None.
                  Actual Behavior
                  Revealed type is object.
                  I made some additional tests:
                  • pyright gives A | B | None (good).
                  • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
                  • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
                  • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
                  • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
                  Your Environment
                  • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
                  • Mypy command-line flags: --strict.
                  • Mypy configuration options from mypy.ini (and other config files):
                  • Python version used: 3.9, 3.10
                  • Operating system and version: Arch Linux
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      Attribute of type A | B | None becomes object after narrowing checks #12009
                      Closed
                      Closed
                      Attribute of type A | B | None becomes object after narrowing checks#12009
                      Labels
                      bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                      Description
                      @bluetech
                      bluetech
                      opened on Jan 18, 2022
                      Bug Report
                      When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
                      To Reproduce
                      The following is the most minimal reproduction I was able to create.
                      classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
                      Expected Behavior
                      Revealed type is A | B | None.
                      Actual Behavior
                      Revealed type is object.
                      I made some additional tests:
                      • pyright gives A | B | None (good).
                      • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
                      • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
                      • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
                      • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
                      Your Environment
                      • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
                      • Mypy command-line flags: --strict.
                      • Mypy configuration options from mypy.ini (and other config files):
                      • Python version used: 3.9, 3.10
                      • Operating system and version: Arch Linux
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                          Skip to content
                          Attribute of type A | B | None becomes object after narrowing checks #12009
                          Closed
                          Closed
                          Attribute of type A | B | None becomes object after narrowing checks#12009
                          Labels
                          bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                          Description
                          @bluetech
                          bluetech
                          opened on Jan 18, 2022
                          Bug Report
                          When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
                          To Reproduce
                          The following is the most minimal reproduction I was able to create.
                          classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
                          Expected Behavior
                          Revealed type is A | B | None.
                          Actual Behavior
                          Revealed type is object.
                          I made some additional tests:
                          • pyright gives A | B | None (good).
                          • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
                          • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
                          • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
                          • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
                          Your Environment
                          • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
                          • Mypy command-line flags: --strict.
                          • Mypy configuration options from mypy.ini (and other config files):
                          • Python version used: 3.9, 3.10
                          • Operating system and version: Arch Linux
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

                              Skip to content
                              Attribute of type A | B | None becomes object after narrowing checks #12009
                              Closed
                              Closed
                              Attribute of type A | B | None becomes object after narrowing checks#12009
                              Labels
                              bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
                              Description
                              @bluetech
                              bluetech
                              opened on Jan 18, 2022
                              Bug Report
                              When doing narrowing of a class attribute with a particular type shape A | B | None, the type of the attribute becomes object after the narrowing condition chain.
                              To Reproduce
                              The following is the most minimal reproduction I was able to create.
                              classA: passclassB: passclassC:
attr: A|B|Nonec=C()
ifc.attrisNone: passelifisinstance(c.attr, A): passelifisinstance(c.attr, B): pass# Optional line - no difference if removedreveal_type(c.attr)
                              Expected Behavior
                              Revealed type is A | B | None.
                              Actual Behavior
                              Revealed type is object.
                              I made some additional tests:
                              • pyright gives A | B | None (good).
                              • Doing x = c.x and then doing the narrowing and reveal_type on attr gives A | B | None (good).
                              • Replacing the None with A | B | D gives A | B | D (good). Also if I replace if isinstance(c.attr, D) with if type(c.attr) is D (good). So the None seems essential.
                              • With just attr: A | None, gives A | None (good). So more than one type besides the None seems essential.
                              • Changing the elif -> if gives A | B | None (good). So the elif seems essential.
                              Your Environment
                              • Mypy version used: master, 0.931, 0.900 (didn't try earlier versions).
                              • Mypy command-line flags: --strict.
                              • Mypy configuration options from mypy.ini (and other config files):
                              • Python version used: 3.9, 3.10
                              • Operating system and version: Arch Linux
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                                bugmypy got something wrongtopic-join-v-unionUsing join vs. using unions
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