Skip to content

cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387

Open
Open
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
Labels
CS50PCS50 Python

Description

@kali-mx
kali-mx
opened on Dec 1, 2025

Summary

Raising this to help improve the autograder tests for future students.

For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.

This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."

Minimal example

Here is a (deliberately incorrect) implementation of count:

defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally

With this implementation:

>>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.

Expected vs actual behavior

Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.

Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.

Image

Metadata

Metadata

Assignees

No one assigned

    Labels

    CS50PCS50 Python

    Type

    No type

    Projects

    No projects

      Milestone

      No milestone

      Relationships

      None yet

      Development

      No branches or pull requests

      Issue actions

      , 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
       blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
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;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
      Skip to content
      cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
      Open
      Open
      cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
      Labels
      CS50PCS50 Python
      Description
      @kali-mx
      kali-mx
      opened on Dec 1, 2025
      Summary
      Raising this to help improve the autograder tests for future students.
      For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
      This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
      Minimal example
      Here is a (deliberately incorrect) implementation of count:
      defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
      With this implementation:
      >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

      Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
      Expected vs actual behavior
      Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
      Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
      Image
      Metadata
      Metadata
      Assignees
      No one assigned
        Labels
        CS50PCS50 Python
        Type
        No type
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
          Skip to content
          cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
          Open
          Open
          cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
          Labels
          CS50PCS50 Python
          Description
          @kali-mx
          kali-mx
          opened on Dec 1, 2025
          Summary
          Raising this to help improve the autograder tests for future students.
          For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
          This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
          Minimal example
          Here is a (deliberately incorrect) implementation of count:
          defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
          With this implementation:
          >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

          Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
          Expected vs actual behavior
          Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
          Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
          Image
          Metadata
          Metadata
          Assignees
          No one assigned
            Labels
            CS50PCS50 Python
            Type
            No type
            Projects
            No projects
              Milestone
              No milestone
              Relationships
              None yet
              Development
              No branches or pull requests
              Issue actions
              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
              Skip to content
              cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
              Open
              Open
              cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
              Labels
              CS50PCS50 Python
              Description
              @kali-mx
              kali-mx
              opened on Dec 1, 2025
              Summary
              Raising this to help improve the autograder tests for future students.
              For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
              This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
              Minimal example
              Here is a (deliberately incorrect) implementation of count:
              defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
              With this implementation:
              >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

              Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
              Expected vs actual behavior
              Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
              Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
              Image
              Metadata
              Metadata
              Assignees
              No one assigned
                Labels
                CS50PCS50 Python
                Type
                No type
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions
                  
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
                  Skip to content
                  cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
                  Open
                  Open
                  cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
                  Labels
                  CS50PCS50 Python
                  Description
                  @kali-mx
                  kali-mx
                  opened on Dec 1, 2025
                  Summary
                  Raising this to help improve the autograder tests for future students.
                  For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
                  This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
                  Minimal example
                  Here is a (deliberately incorrect) implementation of count:
                  defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
                  With this implementation:
                  >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

                  Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
                  Expected vs actual behavior
                  Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
                  Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
                  Image
                  Metadata
                  Metadata
                  Assignees
                  No one assigned
                    Labels
                    CS50PCS50 Python
                    Type
                    No type
                    Projects
                    No projects
                      Milestone
                      No milestone
                      Relationships
                      None yet
                      Development
                      No branches or pull requests
                      Issue actions
                      
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
                      Skip to content
                      cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
                      Open
                      Open
                      cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
                      Labels
                      CS50PCS50 Python
                      Description
                      @kali-mx
                      kali-mx
                      opened on Dec 1, 2025
                      Summary
                      Raising this to help improve the autograder tests for future students.
                      For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
                      This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
                      Minimal example
                      Here is a (deliberately incorrect) implementation of count:
                      defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
                      With this implementation:
                      >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

                      Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
                      Expected vs actual behavior
                      Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
                      Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
                      Image
                      Metadata
                      Metadata
                      Assignees
                      No one assigned
                        Labels
                        CS50PCS50 Python
                        Type
                        No type
                        Projects
                        No projects
                          Milestone
                          No milestone
                          Relationships
                          None yet
                          Development
                          No branches or pull requests
                          Issue actions
                          
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
                          Skip to content
                          cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
                          Open
                          Open
                          cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
                          Labels
                          CS50PCS50 Python
                          Description
                          @kali-mx
                          kali-mx
                          opened on Dec 1, 2025
                          Summary
                          Raising this to help improve the autograder tests for future students.
                          For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
                          This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
                          Minimal example
                          Here is a (deliberately incorrect) implementation of count:
                          defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
                          With this implementation:
                          >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

                          Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
                          Expected vs actual behavior
                          Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
                          Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
                          Image
                          Metadata
                          Metadata
                          Assignees
                          No one assigned
                            Labels
                            CS50PCS50 Python
                            Type
                            No type
                            Projects
                            No projects
                              Milestone
                              No milestone
                              Relationships
                              None yet
                              Development
                              No branches or pull requests
                              Issue actions
                              
, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();
cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" · Issue #387 · cs50/problems · GitHub
                              Skip to content
                              cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um" #387
                              Open
                              Open
                              cs50/problems/2022/python/um: check50 accepts substring-based solution that counts words like "umbrella" as "um"#387
                              Labels
                              CS50PCS50 Python
                              Description
                              @kali-mx
                              kali-mx
                              opened on Dec 1, 2025
                              Summary
                              Raising this to help improve the autograder tests for future students.
                              For cs50/problems/2022/python/um, check50 currently accepts a count implementation that treats "um" as a prefix/substring rather than a whole word. As a result, count("umbrella") returns 1, but check50 cs50/problems/2022/python/um still passes.
                              This appears to contradict the spec, which states that "um" should be counted only "as a word unto itself, not as a substring of some other word."
                              Minimal example
                              Here is a (deliberately incorrect) implementation of count:
                              defcount(s):
tally=0pieces=s.split(" ")
foriteminpieces:
ifitem.lower().startswith("umm"):
continueifitem.lower().startswith("um"):
tally+=1returntally
                              With this implementation:
                              >>> count("um")
1
>>> count("Um, thanks, um...")
2
>>> count("umbrella")
1 # <-- incorrect per spec, but not caught by check50

                              Despite this clearly incorrect behavior for "umbrella" (and other words like "umlaut" or "umami"), check50 cs50/problems/2022/python/um reports all tests passing.
                              Expected vs actual behavior
                              Expected: check50 should fail implementations that count "um" inside larger words, per the problem specification.
                              Actual: A substring-/prefix-based implementation like the one above passes all check50 tests.
                              Image
                              Metadata
                              Metadata
                              Assignees
                              No one assigned
                                Labels
                                CS50PCS50 Python
                                Type
                                No type
                                Projects
                                No projects
                                  Milestone
                                  No milestone
                                  Relationships
                                  None yet
                                  Development
                                  No branches or pull requests
                                  Issue actions