{"id":24133,"date":"2022-11-30T16:20:56","date_gmt":"2022-11-30T10:50:56","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-python-i-want-a-different-way-of-doing-this-while-loop-closed\/"},"modified":"2022-11-30T16:20:56","modified_gmt":"2022-11-30T10:50:56","slug":"solved-python-i-want-a-different-way-of-doing-this-while-loop-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-python-i-want-a-different-way-of-doing-this-while-loop-closed\/","title":{"rendered":"[Solved] Python I want a different way of doing this while loop [closed]"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-21345107\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"21345107\" data-parentid=\"21344917\" data-score=\"0\" data-position-on-page=\"2\" data-highest-scored=\"0\" data-question-has-accepted-highest-score=\"0\" itemprop=\"suggestedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>If just want to handle <code>\"quit\"<\/code> or a float, that&#8217;s easy:<\/p>\n<pre><code>total = 0.0\nwhile True:\n    value = raw_input(\"enter a number or quit to finish\"))\n    if value == \"quit\":\n        break\n    total += float(value)\nprint total\n<\/code><\/pre>\n<p>But if the user types, say, <code>qiut<\/code> or <code>2..137<\/code>, the program will bail out with a <code>ValueError<\/code>. How do you protect against that, without a <code>try<\/code>?<\/p>\n<p>Or, what if you want to prevent the user from entering, say, <code>inf<\/code> or <code>-inf<\/code> or <code>nan<\/code>, or something that will (at least on some platforms) overflow to one of those (e.g., try <code>1e309<\/code> on most systems)?<\/p>\n<p>Well, you need some way to verify that the <code>float<\/code> call is going to work in advance.<\/p>\n<p>First, you have to parse <a rel=\"nofollow noopener\" target=\"_blank\" href=\"http:\/\/docs.python.org\/2\/reference\/lexical_analysis.html#floating-point-literals\">Python 2.7&#8217;s floating point literal syntax<\/a>. At least you&#8217;re not dealing with Python 3.x, where, e.g., <code>float('\u0661\u0660\u0663')<\/code> is perfectly valid and means <code>103.0<\/code>. The language is easily translatable to a regular language, meaning <code>re<\/code> or plain string methods should be enough, or you can implement the grammar with something like <a rel=\"nofollow noopener\" target=\"_blank\" href=\"http:\/\/pyparsing.wikispaces.com\"><code>PyParsing<\/code><\/a> or a hand-rolled recursive descent parser instead of translating.<\/p>\n<p>Next, you need to evaluate the value to make sure it&#8217;s not going to give an error when evaluated as a float. <a rel=\"nofollow noopener\" target=\"_blank\" href=\"http:\/\/docs.python.org\/2\/library\/sys.html#sys.float_info\"><code>sys.float_info<\/code><\/a> should have all the information you need\u2026 except that Python 2.7 doesn&#8217;t actually define what is and isn&#8217;t an error. In general, overflow automatically turns into <code>inf<\/code> or <code>-inf<\/code>, and underflow to <code>0<\/code>, but you may need a bit of trial and error to see what it does for all the edge cases (or, alternatively, look over your interpreter&#8217;s source code).<\/p>\n<p>You can probably optimize this part by first ruling in and out everything that&#8217;s clearly illegal\/safe (e.g., if there&#8217;s no exponent and the length is short enough, it can&#8217;t possibly overflow), but there will be some range you will have to check in detail.<\/p>\n<p>Or, while you&#8217;re evaluating the number, you might as well skip the <code>float<\/code> anyway, and just use the number you evaluated. That even allows you to use <em>different<\/em> rules from Python 2.7 if you want (e.g., handle Persian numerals, or forms like <code>1.2x10^3<\/code> instead of just <code>1.2e3<\/code>, or allow thousands separators, or\u2026).<\/p>\n<p>I won&#8217;t write the code for you, because this would all be an insane thing to do. It will take a lot of design, coding, testing, and debugging, and in the end it will run a few orders of magnitude slower than just letting Python <code>try<\/code> the <code>float<\/code> for you.<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\"><\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved Python I want a different way of doing this while loop [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] If just want to handle &#8220;quit&#8221; or a float, that&#8217;s easy: total = 0.0 while True: value = raw_input(&#8220;enter a number or quit to finish&#8221;)) if value == &#8220;quit&#8221;: break total += float(value) print total But if the user types, say, qiut or 2..137, the program will bail out with a ValueError. How do &#8230; <a title=\"[Solved] Python I want a different way of doing this while loop [closed]\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-python-i-want-a-different-way-of-doing-this-while-loop-closed\/\" aria-label=\"More on [Solved] Python I want a different way of doing this while loop [closed]\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[391,349,1314,459],"class_list":["post-24133","post","type-post","status-publish","format-standard","hentry","category-solved","tag-loops","tag-python","tag-try-catch","tag-while-loop"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] Python I want a different way of doing this while loop [closed] - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-python-i-want-a-different-way-of-doing-this-while-loop-closed\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Python I want a different way of doing this while loop [closed] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] If just want to handle &quot;quit&quot; or a float, that&#8217;s easy: total = 0.0 while True: value = raw_input(&quot;enter a number or quit to finish&quot;)) if value == &quot;quit&quot;: break total += float(value) print total But if the user types, say, qiut or 2..137, the program will bail out with a ValueError. How do ... 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