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今天小编给大家分享一下web开发中怎么编写可读代码的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。
“Code should be written to minimize the time it would take for someone else to understand it.”
日常工作的事实是：
写代码前的思考和看代码的时间远大于真正写的时间
读代码是很平常的事情，不论是别人的，还是自己的，半年前写的可认为是别人的代码
代码可读性高，很快就可以理解程序的逻辑，进入工作状态
行数少的代码不一定就容易理解
代码的可读性与程序的效率、架构、易于测试一点也不冲突
整本书都围绕“如何让代码的可读性更高”这个目标来写。这也是好代码的重要标准之一。
使用含义明确的词，比如用download而不是get，参考以下替换方案：
send -> deliver, dispatch, announce, distribute, route find -> search, extract, locate, recoverstart -> lanuch, create, begin, open make -> create,set up, build, generate, compose, add, new
像tmp和retval这样词，除了说明是临时变量和返回值之外，没有任何意义。但是给他加一些有意义的词，就会很明确：
tmp_file = tempfile.NamedTemporaryFile() ...SaveData(tmp_file, ...)
不使用retval而使用变量真正代表的意义：
sum_squares += v[i]; // Where's the "square" that we're summing? Bug!
嵌套的for循环中,i、j也有同样让人困惑的时候：
for (int i = 0; i < clubs.size(); i++) for (int j = 0; j < clubs[i].members.size(); j++) for (int k = 0; k < users.size(); k++) if (clubs[i].members[k] == users[j]) cout << "user[" << j << "] is in club[" << i << "]" << endl;
换一种写法就会清晰很多：
if (clubs[ci].members[mi] == users[ui]) # OK. First letters match.
所以，当使用一些通用的词，要有充分的理由才可以。
CanListenOnPort就比ServerCanStart好，can start比较含糊，而listen on port确切的说明了这个方法将要做什么。
--run_locally就不如--extra_logging来的明确。
_ms，对原始字符串加_raw如果一个变量很重要，那么在名字上多加一些额外的字就会更加易读，比如将string id; // Example: "af84ef845cd8"换成string hex_id;。
Start(int delay) --> delay → delay_secs CreateCache(int size) --> size → size_mbThrottleDownload(float limit) --> limit → max_kbps Rotate(float angle) --> angle → degrees_cw
更多例子：
password -> plaintext_password comment -> unescaped_comment html -> html_utf8 data -> data_urlenc
在比较小的作用域内，可以使用较短的变量名，在较大的作用域内使用的变量，最好用长一点的名字，编辑器的自动补全都可以很好的减少键盘输入。对于一些缩写前缀，尽量选择众所周知的(如str)，一个判断标准是，当新成员加入时，是否可以无需他人帮助而明白前缀代表什么。
_、-等符号，比如对私有变量加_前缀。var x = new DatePicker(); // DatePicker() 是类的"构造"函数，大写开始var y = pageHeight(); // pageHeight() 是一个普通函数 var $all_images = $("img"); // $all_images 是jQuery对象var height = 250; // height不是 //id和class的写法分开<div id="middle_column" class="main-content"> ...命名的时候可以先想一下，我要用的这个词是否有别的含义。举个例子：
results = Database.all_objects.filter("year <= 2011")现在的结果到底是包含2011年之前的呢还是不包含呢？
min、max代替limitCART_TOO_BIG_LIMIT = 10 if shopping_cart.num_items() >= CART_TOO_BIG_LIMIT: Error("Too many items in cart.") MAX_ITEMS_IN_CART = 10 if shopping_cart.num_items() > MAX_ITEMS_IN_CART: Error("Too many items in cart.")对比上例中CART_TOO_BIG_LIMIT和MAX_ITEMS_IN_CART，想想哪个更好呢？
first和last来表示闭区间print integer_range(start=2, stop=4)# Does this print [2,3] or [2,3,4] (or something else)? set.PrintKeys(first="Bart", last="Maggie")
first和last含义明确，适宜表示闭区间。
beigin和end表示前闭后开(2,9))区间PrintEventsInRange("OCT 16 12:00am", "OCT 17 12:00am") PrintEventsInRange("OCT 16 12:00am", "OCT 16 11:59:59.9999pm")上面一种写法就比下面的舒服多了。
bool read_password = true;
这是一个很危险的命名，到底是需要读取密码呢，还是密码已经被读取呢，不知道，所以这个变量可以使用user_is_authenticated代替。通常，给Boolean型变量添加is、has、can、should可以让含义更清晰，比如：
SpaceLeft() --> hasSpaceLeft()bool disable_ssl = false --> bool use_ssl = true
public class StatisticsCollector { public void addSample(double x) { ... } public double getMean() { // Iterate through all samples and return total / num_samples } ...}在这个例子中，getMean方法遍历了所有的样本，返回总额，所以并不是普通意义上轻量的get方法，所以应该取名computeMean比较合适。
写出来漂亮的格式，充满美感，读起来自然也会舒服很多，对比下面两个例子：
class StatsKeeper { public: // A class for keeping track of a series of doubles void Add(double d); // and methods for quick statistics about them private: int count; /* how many so far */ public: double Average(); private: double minimum; list<double> past_items ;double maximum;};什么是充满美感的呢：
// A class for keeping track of a series of doubles// and methods for quick statistics about them.class StatsKeeper { public: void Add(double d); double Average(); private: list<double> past_items; int count; // how many so far double minimum; double maximum;};这段代码需要断行，来满足不超过一行80个字符的要求，参数也需要注释说明：
public class PerformanceTester { public static final TcpConnectionSimulator wifi = new TcpConnectionSimulator( 500, /* Kbps */ 80, /* millisecs latency */ 200, /* jitter */ 1 /* packet loss % */); public static final TcpConnectionSimulator t3_fiber = new TcpConnectionSimulator( 45000, /* Kbps */ 10, /* millisecs latency */ 0, /* jitter */ 0 /* packet loss % */); public static final TcpConnectionSimulator cell = new TcpConnectionSimulator( 100, /* Kbps */ 400, /* millisecs latency */ 250, /* jitter */ 5 /* packet loss % */);}考虑到代码的连贯性，先优化成这样：
public class PerformanceTester { public static final TcpConnectionSimulator wifi = new TcpConnectionSimulator( 500, /* Kbps */ 80, /* millisecs latency */ 200, /* jitter */ 1 /* packet loss % */); public static final TcpConnectionSimulator t3_fiber = new TcpConnectionSimulator( 45000, /* Kbps */ 10, /* millisecs latency */ 0, /* jitter */ 0 /* packet loss % */); public static final TcpConnectionSimulator cell = new TcpConnectionSimulator( 100, /* Kbps */ 400, /* millisecs latency */ 250, /* jitter */ 5 /* packet loss % */);}连贯性好一点，但还是太罗嗦，额外占用很多空间：
public class PerformanceTester { // TcpConnectionSimulator(throughput, latency, jitter, packet_loss) // [Kbps] [ms] [ms] [percent] public static final TcpConnectionSimulator wifi = new TcpConnectionSimulator(500, 80, 200, 1); public static final TcpConnectionSimulator t3_fiber = new TcpConnectionSimulator(45000, 10, 0, 0); public static final TcpConnectionSimulator cell = new TcpConnectionSimulator(100, 400, 250, 5);}// Turn a partial_name like "Doug Adams" into "Mr. Douglas Adams".// If not possible, 'error' is filled with an explanation.string ExpandFullName(DatabaseConnection dc, string partial_name, string* error); DatabaseConnection database_connection;string error;assert(ExpandFullName(database_connection, "Doug Adams", &error) == "Mr. Douglas Adams");assert(error == "");assert(ExpandFullName(database_connection, " Jake Brown ", &error) == "Mr. Jacob Brown III");assert(error == "");assert(ExpandFullName(database_connection, "No Such Guy", &error) == "");assert(error == "no match found");assert(ExpandFullName(database_connection, "John", &error) == "");assert(error == "more than one result");
上面这段代码看起来很脏乱，很多重复性的东西，可以用函数封装：
CheckFullName("Doug Adams", "Mr. Douglas Adams", "");CheckFullName(" Jake Brown ", "Mr. Jake Brown III", "");CheckFullName("No Such Guy", "", "no match found");CheckFullName("John", "", "more than one result"); void CheckFullName(string partial_name, string expected_full_name, string expected_error) { // database_connection is now a class member string error; string full_name = ExpandFullName(database_connection, partial_name, &error); assert(error == expected_error); assert(full_name == expected_full_name);}列对齐可以让代码段看起来更舒适：
CheckFullName("Doug Adams" , "Mr. Douglas Adams" , "");CheckFullName(" Jake Brown ", "Mr. Jake Brown III", "");CheckFullName("No Such Guy" , "" , "no match found");CheckFullName("John" , "" , "more than one result"); commands[] = { ... { "timeout" , NULL , cmd_spec_timeout}, { "timestamping" , &opt.timestamping , cmd_boolean}, { "tries" , &opt.ntry , cmd_number_inf}, { "useproxy" , &opt.use_proxy , cmd_boolean}, { "useragent" , NULL , cmd_spec_useragent}, ...};class FrontendServer { public: FrontendServer(); void ViewProfile(HttpRequest* request); void OpenDatabase(string location, string user); void SaveProfile(HttpRequest* request); string ExtractQueryParam(HttpRequest* request, string param); void ReplyOK(HttpRequest* request, string html); void FindFriends(HttpRequest* request); void ReplyNotFound(HttpRequest* request, string error); void CloseDatabase(string location); ~FrontendServer();};上面这一段虽然能看，不过还有优化空间：
class FrontendServer { public: FrontendServer(); ~FrontendServer(); // Handlers void ViewProfile(HttpRequest* request); void SaveProfile(HttpRequest* request); void FindFriends(HttpRequest* request); // Request/Reply Utilities string ExtractQueryParam(HttpRequest* request, string param); void ReplyOK(HttpRequest* request, string html); void ReplyNotFound(HttpRequest* request, string error); // Database Helpers void OpenDatabase(string location, string user); void CloseDatabase(string location);};再来看一段代码：
# Import the user's email contacts, and match them to users in our system.# Then display a list of those users that he/she isn't already friends with.def suggest_new_friends(user, email_password): friends = user.friends() friend_emails = set(f.email for f in friends) contacts = import_contacts(user.email, email_password) contact_emails = set(c.email for c in contacts) non_friend_emails = contact_emails - friend_emails suggested_friends = User.objects.select(email__in=non_friend_emails) display['user'] = user display['friends'] = friends display['suggested_friends'] = suggested_friends return render("suggested_friends.html", display)全都混在一起，视觉压力相当大，按功能化块：
def suggest_new_friends(user, email_password): # Get the user's friends' email addresses. friends = user.friends() friend_emails = set(f.email for f in friends) # Import all email addresses from this user's email account. contacts = import_contacts(user.email, email_password) contact_emails = set(c.email for c in contacts) # Find matching users that they aren't already friends with. non_friend_emails = contact_emails - friend_emails suggested_friends = User.objects.select(email__in=non_friend_emails) # Display these lists on the page. display['user'] = user display['friends'] = friends display['suggested_friends'] = suggested_friends return render("suggested_friends.html", display)让代码看起来更舒服，需要在写的过程中多注意，培养一些好的习惯，尤其当团队合作的时候，代码风格比如大括号的位置并没有对错，但是不遵循团队规范那就是错的。
当你写代码的时候，你会思考很多，但是最终呈现给读者的就只剩代码本身了，额外的信息丢失了，所以注释的目的就是让读者了解更多的信息。
这样的注释毫无价值：
// The class definition for Accountclass Account { public: // Constructor Account(); // Set the profit member to a new value void SetProfit(double profit); // Return the profit from this Account double GetProfit();};// Find a Node with the given 'name' or return NULL.// If depth <= 0, only 'subtree' is inspected.// If depth == N, only 'subtree' and N levels below are inspected.Node* FindNodeInSubtree(Node* subtree, string name, int depth);
// Enforce limits on the Reply as stated in the Request,// such as the number of items returned, or total byte size, etc. void CleanReply(Request request, Reply reply);
注释的大部分都在解释clean是什么意思，那不如换个正确的名字：
// Make sure 'reply' meets the count/byte/etc. limits from the 'request' void EnforceLimitsFromRequest(Request request, Reply reply);
我们讨论了不该注释什么，那么应该注释什么呢？注释应该记录你思考代码怎么写的结果，比如像下面这些：
// Surprisingly, a binary tree was 40% faster than a hash table for this data.// The cost of computing a hash was more than the left/right comparisons. // This heuristic might miss a few words. That's OK; solving this 100% is hard. // This class is getting messy. Maybe we should create a 'ResourceNode' subclass to// help organize things.
也可以用来记录流程和常量：
// TODO: use a faster algorithm// TODO(dustin): handle other image formats besides JPEG NUM_THREADS = 8 # as long as it's >= 2 * num_processors, that's good enough. // Impose a reasonable limit - no human can read that much anyway.const int MAX_RSS_SUBSCRIPTIONS = 1000;
可用的词有：
TODO : Stuff I haven't gotten around to yetFIXME : Known-broken code hereHACK : Adimittedly inelegant solution to a problemXXX : Danger! Major problem here
当别人读你的代码时，让他们产生疑问的部分，就是你应该注释的地方。
struct Recorder { vector<float> data; ... void Clear() { vector<float>().swap(data); // Huh? Why not just data.clear()? }};很多C++的程序员啊看到这里，可能会想为什么不用data.clear()来代替vector.swap，所以那个地方应该加上注释：
// Force vector to relinquish its memory (look up "STL swap trick")vector<float>().swap(data);
你在写代码的过程中，可能用到一些hack，或者有其他需要读代码的人知道的陷阱，这时候就应该注释：
void SendEmail(string to, string subject, string body);
而实际上这个发送邮件的函数是调用别的服务，有超时设置，所以需要注释：
// Calls an external service to deliver email. (Times out after 1 minute.)void SendEmail(string to, string subject, string body);
有时候为了更清楚说明，需要给整个文件加注释，让读者有个总体的概念：
// This file contains helper functions that provide a more convenient interface to our// file system. It handles file permissions and other nitty-gritty details.
即使是在函数内部，也可以有类似文件注释那样的说明注释：
# Find all the items that customers purchased for themselves.for customer_id in all_customers: for sale in all_sales[customer_id].sales: if sale.recipient == customer_id: ...
或者按照函数的步进，写一些注释：
def GenerateUserReport(): # Acquire a lock for this user ... # Read user's info from the database ... # Write info to a file ... # Release the lock for this user
很多人不愿意写注释，确实，要写好注释也不是一件简单的事情，也可以在文件专门的地方，留个写注释的区域，可以写下你任何想说的东西。
前一个小节讨论了注释应该写什么，这一节来讨论应该怎么写，因为注释很重要，所以要写的精确，注释也占据屏幕空间，所以要简洁。
// The int is the CategoryType.// The first float in the inner pair is the 'score',// the second is the 'weight'.typedef hash_map<int, pair<float, float> > ScoreMap;
这样写太罗嗦了，尽量精简压缩成这样：
// CategoryType -> (score, weight)typedef hash_map<int, pair<float, float> > ScoreMap;
// Insert the data into the cache, but check if it's too big first.
这里的it's有歧义，不知道所指的是data还是cache，改成如下：
// Insert the data into the cache, but check if the data is too big first.
还有更好的解决办法，这里的it就有明确所指：
// If the data is small enough, insert it into the cache.
# Depending on whether we've already crawled this URL before, give it a different priority.
这句话理解起来太费劲，改成如下就好理解很多：
# Give higher priority to URLs we've never crawled before.
// Return the number of lines in this file.int CountLines(string filename) { ... }这样的一个函数，用起来可能会一头雾水，因为他可以有很多歧义：
”” 一个空文件，是0行还是1行？
“hello” 只有一行，那么返回值是0还是1？
“hello\n” 这种情况返回1还是2？
“hello\n world” 返回1还是2？
“hello\n\r cruel\n world\r” 返回2、3、4哪一个呢？
所以注释应该这样写：
// Count how many newline bytes ('\n') are in the file.int CountLines(string filename) { ... }// Rearrange 'v' so that elements < pivot come before those >= pivot;// Then return the largest 'i' for which v[i] < pivot (or -1 if none are < pivot)int Partition(vector<int>* v, int pivot);
这个描述很精确，但是如果再加入一个例子，就更好了：
// ...// Example: Partition([8 5 9 8 2], 8) might result in [5 2 | 8 9 8] and return 1int Partition(vector<int>* v, int pivot);
void DisplayProducts(list<Product> products) { products.sort(CompareProductByPrice); // Iterate through the list in reverse order for (list<Product>::reverse_iterator it = products.rbegin(); it != products.rend(); ++it) DisplayPrice(it->price); ... }这里的注释说明了倒序排列，单还不够准确，应该改成这样：
// Display each price, from highest to lowestfor (list<Product>::reverse_iterator it = products.rbegin(); ... )
看见这样的一个函数调用，肯定会一头雾水：
Connect(10, false);
如果加上这样的注释，读起来就清楚多了：
def Connect(timeout, use_encryption): ... # Call the function using named parametersConnect(timeout = 10, use_encryption = False)
// This class contains a number of members that store the same information as in the// database, but are stored here for speed. When this class is read from later, those// members are checked first to see if they exist, and if so are returned; otherwise the// database is read from and that data stored in those fields for next time.
上面这一大段注释，解释的很清楚，如果换一个词来代替，也不会有什么疑惑：
// This class acts as a caching layer to the database.
让条件语句、循环以及其他控制流程的代码尽可能自然，让读者在阅读过程中不需要停顿思考或者在回头查找，是这一节的目的。
对比下面两种条件的写法：
if (length >= 10)while (bytes_received < bytes_expected) if (10 <= length)while (bytes_expected > bytes_received)
到底是应该按照大于小于的顺序来呢，还是有其他的准则？是的，应该按照参数的意义来
运算符左边：通常是需要被检查的变量，也就是会经常变化的
运算符右边：通常是被比对的样本，一定程度上的常量
这就解释了为什么bytes_received < bytes_expected比反过来更好理解。
通常，if/else的顺序你可以自由选择，下面这两种都可以：
if (a == b) { // Case One ...} else { // Case Two ...} if (a != b) { // Case Two ...} else { // Case One ...}或许对此你也没有仔细斟酌过，但在有些时候，一种顺序确实好过另一种：
正向的逻辑在前，比如if(debug)就比if(!debug)好
简单逻辑的在前，这样if和else就可以在一个屏幕显示 - 有趣、清晰的逻辑在前
举个例子来看：
if (!url.HasQueryParameter("expand_all")) { response.Render(items); ...} else { for (int i = 0; i < items.size(); i++) { items[i].Expand(); } ... }看到if你首先想到的是expand_all，就好像告诉你“不要想大象”，你会忍不住去想它，所以产生了一点点迷惑，最好写成：
if (url.HasQueryParameter("expand_all")) { for (int i = 0; i < items.size(); i++) { items[i].Expand(); } ... } else { response.Render(items); ... }time_str += (hour >= 12) ? "pm" : "am"; Avoiding the ternary operator, you might write: if (hour >= 12) { time_str += "pm"; } else { time_str += "am";}使用三目运算符可以减少代码行数，上例就是一个很好的例证，但是我们的真正目的是减少读代码的时间，所以下面的情况并不适合用三目运算符：
return exponent >= 0 ? mantissa * (1 << exponent) : mantissa / (1 << -exponent); if (exponent >= 0) { return mantissa * (1 << exponent);} else { return mantissa / (1 << -exponent);}所以只在简单表达式的地方用。
do { continue;} while (false);这段代码会执行几遍呢，需要时间思考一下，do/while完全可以用别的方法代替，所以应避免使用。
public boolean Contains(String str, String substr) { if (str == null || substr == null) return false; if (substr.equals("")) return true; ...}函数里面尽早的return，可以让逻辑更加清晰。
if (user_result == SUCCESS) { if (permission_result != SUCCESS) { reply.WriteErrors("error reading permissions"); reply.Done(); return; } reply.WriteErrors("");} else { reply.WriteErrors(user_result);}reply.Done();这样一段代码，有一层的嵌套，但是看起来也会稍有迷惑，想想自己的代码，有没有类似的情况呢？可以换个思路去考虑这段代码，并且用尽早return的原则修改，看起来就舒服很多：
if (user_result != SUCCESS) { reply.WriteErrors(user_result); reply.Done(); return;}if (permission_result != SUCCESS) { reply.WriteErrors(permission_result); reply.Done(); return;}reply.WriteErrors("");reply.Done();同样的，对于有嵌套的循环，可以采用同样的办法：
for (int i = 0; i < results.size(); i++) { if (results[i] != NULL) { non_null_count++; if (results[i]->name != "") { cout << "Considering candidate..." << endl; ... } }}换一种写法，尽早return，在循环中就用continue：
for (int i = 0; i < results.size(); i++) { if (results[i] == NULL) continue; non_null_count++; if (results[i]->name == "") continue; cout << "Considering candidate..." << endl; ... }很显然的，越复杂的表达式，读起来越费劲，所以应该把那些复杂而庞大的表达式，拆分成一个个易于理解的小式子。
将复杂表达式拆分最简单的办法，就是增加一个变量：
if line.split(':')[0].strip() == "root": //用变量替换username = line.split(':')[0].strip() if username == "root": ...或者这个例子：
if (request.user.id == document.owner_id) { // user can edit this document...}...if (request.user.id != document.owner_id) {// document is read-only...} //用变量替换final boolean user_owns_document = (request.user.id == document.owner_id);if (user_owns_document) { // user can edit this document...}...if (!user_owns_document) { // document is read-only...}1) not (a or b or c) <–> (not a) and (not b) and (not c)
2) not (a and b and c) <–> (not a) or (not b) or (not c)
所以，就可以这样写：
if (!(file_exists && !is_protected)) Error("Sorry, could not read file."); //替换if (!file_exists || is_protected) Error("Sorry, could not read file.");assert((!(bucket = FindBucket(key))) || !bucket->IsOccupied());
这样的代码完全可以用下面这个替换，虽然有两行，但是更易懂：
bucket = FindBucket(key);if (bucket != NULL) assert(!bucket->IsOccupied());
像下面这样的表达式，最好也不要写，因为在有些语言中，x会被赋予第一个为true的变量的值：
x = a || b || c
var update_highlight = function (message_num) { if ($("#vote_value" + message_num).html() === "Up") { $("#thumbs_up" + message_num).addClass("highlighted"); $("#thumbs_down" + message_num).removeClass("highlighted"); } else if ($("#vote_value" + message_num).html() === "Down") { $("#thumbs_up" + message_num).removeClass("highlighted"); $("#thumbs_down" + message_num).addClass("highlighted"); } else { $("#thumbs_up" + message_num).removeClass("highighted"); $("#thumbs_down" + message_num).removeClass("highlighted"); }};这里面有很多重复的语句，我们可以用变量还替换简化：
var update_highlight = function (message_num) { var thumbs_up = $("#thumbs_up" + message_num); var thumbs_down = $("#thumbs_down" + message_num); var vote_value = $("#vote_value" + message_num).html(); var hi = "highlighted"; if (vote_value === "Up") { thumbs_up.addClass(hi); thumbs_down.removeClass(hi); } else if (vote_value === "Down") { thumbs_up.removeClass(hi); thumbs_down.addClass(hi); } else { thumbs_up.removeClass(hi); thumbs_down.removeClass(hi); }}前一节，讲到利用变量来拆解大表达式，这一节来讨论如何消除多余的变量。
now = datetime.datetime.now()root_message.last_view_time = now
这里的now可以去掉，因为：
并非用来拆分复杂的表达式
也没有增加可读性，因为`datetime.datetime.now()`本就清晰
只用了一次
所以完全可以写作：
root_message.last_view_time = datetime.datetime.now()
boolean done = false;while (/* condition */ && !done) { ... if (...) { done = true; continue; }}这里的done可以用别的方式更好的完成：
while (/* condition */) { ... if (...) { break; } }这个例子非常容易修改，如果是比较复杂的嵌套，break可能并不够用，这时候就可以把代码封装到函数中。
我们都听过要避免使用全局变量这样的忠告，是的，当变量的作用域越大，就越难追踪，所以要保持变量小的作用域。
class LargeClass { string str_; void Method1() { str_ = ...; Method2(); } void Method2() { // Uses str_ } // Lots of other methods that don't use str_ ... ;}这里的str_的作用域有些大，完全可以换一种方式：
class LargeClass { void Method1() { string str = ...; Method2(str); } void Method2(string str) { // Uses str } // Now other methods can't see str.};将str通过变量函数参数传递，减小了作用域，也更易读。同样的道理也可以用在定义类的时候，将大类拆分成一个个小类。
# No use of example_value up to this point.if request: for value in request.values: if value > 0: example_value = value break for logger in debug.loggers: logger.log("Example:", example_value)这个例子在运行时候会报example_value is undefined的错，修改起来不算难：
example_value = Noneif request: for value in request.values: if value > 0: example_value = value break if example_value: for logger in debug.loggers: logger.log("Example:", example_value)但是参考前面的消除中间变量准则，还有更好的办法：
def LogExample(value): for logger in debug.loggers: logger.log("Example:", value) if request: for value in request.values: if value > 0: LogExample(value) # deal with 'value' immediately break在C语言中，要求将所有的变量事先声明，这样当用到变量较多时候，读者处理这些信息就会有难度，所以一开始没用到的变量，就暂缓声明：
def ViewFilteredReplies(original_id): filtered_replies = [] root_message = Messages.objects.get(original_id) all_replies = Messages.objects.select(root_id=original_id) root_message.view_count += 1 root_message.last_view_time = datetime.datetime.now() root_message.save() for reply in all_replies: if reply.spam_votes <= MAX_SPAM_VOTES: filtered_replies.append(reply) return filtered_replies
读者一次处理变量太多，可以暂缓声明：
def ViewFilteredReplies(original_id): root_message = Messages.objects.get(original_id) root_message.view_count += 1 root_message.last_view_time = datetime.datetime.now() root_message.save() all_replies = Messages.objects.select(root_id=original_id) filtered_replies = [] for reply in all_replies: if reply.spam_votes <= MAX_SPAM_VOTES: filtered_replies.append(reply) return filtered_replies
前面讨论了过多的变量会让读者迷惑，同一个变量，不停的被赋值也会让读者头晕，如果变量变化的次数少一些，代码可读性就更强。
假设有一个页面，如下，需要给第一个空的input赋值：
<input type="text" id="input1" value="Dustin"><input type="text" id="input2" value="Trevor"><input type="text" id="input3" value=""><input type="text" id="input4" value="Melissa">...var setFirstEmptyInput = function (new_value) { var found = false; var i = 1; var elem = document.getElementById('input' + i); while (elem !== null) { if (elem.value === '') { found = true; break; } i++; elem = document.getElementById('input' + i); } if (found) elem.value = new_value; return elem;};这段代码能工作，有三个变量，我们逐一去看如何优化，found作为中间变量，完全可以消除：
var setFirstEmptyInput = function (new_value) { var i = 1; var elem = document.getElementById('input' + i); while (elem !== null) { if (elem.value === '') { elem.value = new_value; return elem; } i++; elem = document.getElementById('input' + i); } return null;};再来看elem变量，只用来做循环，调用了很多次，所以很难跟踪他的值，i也可以用for来修改：
var setFirstEmptyInput = function (new_value) { for (var i = 1; true; i++) { var elem = document.getElementById('input' + i); if (elem === null) return null; // Search Failed. No empty input found. if (elem.value === '') { elem.value = new_value; return elem; } }};工程师就是将大问题分解为一个个小问题，然后逐个解决，这样也易于保证程序的健壮性、可读性。如何分解子问题，下面给出一些准则：
看看这个方法或代码，问问你自己“这段代码的最终目标是什么？”
对于每一行代码，要问“它与目标直接相关，或者是不相关的子问题？”
如果有足够多行的代码是处理与目标不直接相关的问题，那么抽离成子函数
来看一个例子：
ajax_post({ url: 'http://example.com/submit', data: data, on_success: function (response_data) { var str = "{\n"; for (var key in response_data) { str += " " + key + " = " + response_data[key] + "\n"; } alert(str + "}"); // Continue handling 'response_data' ... }});这段代码的目标是发送一个ajax请求，所以其中字符串处理的部分就可以抽离出来：
var format_pretty = function (obj) { var str = "{\n"; for (var key in obj) { str += " " + key + " = " + obj[key] + "\n"; } return str + "}";};有很多理由将format_pretty抽离出来，这些独立的函数可以很容易的添加feature，增强可靠性，处理边界情况，等等。所以这里，可以将format_pretty增强，就会得到一个更强大的函数：
var format_pretty = function (obj, indent) { // Handle null, undefined, strings, and non-objects. if (obj === null) return "null"; if (obj === undefined) return "undefined"; if (typeof obj === "string") return '"' + obj + '"'; if (typeof obj !== "object") return String(obj); if (indent === undefined) indent = ""; // Handle (non-null) objects. var str = "{\n"; for (var key in obj) { str += indent + " " + key + " = "; str += format_pretty(obj[key], indent + " ") + "\n"; } return str + indent + "}";};这个函数输出：
{ key1 = 1 key2 = true key3 = undefined key4 = null key5 = { key5a = { key5a1 = "hello world" } }}多做这样的事情，就是积累代码的过程，这样的代码可以复用，也可以形成自己的代码库，或者分享给别人。
那些与目标不相关函数，抽离出来可以复用，与业务相关的也可以抽出来，保持代码的易读性，例如：
business = Business()business.name = request.POST["name"] url_path_name = business.name.lower()url_path_name = re.sub(r"['\.]", "", url_path_name) url_path_name = re.sub(r"[^a-z0-9]+", "-", url_path_name) url_path_name = url_path_name.strip("-")business.url = "/biz/" + url_path_name business.date_created = datetime.datetime.utcnow() business.save_to_database()抽离出来，就好看很多：
CHARS_TO_REMOVE = re.compile(r"['\.']+")CHARS_TO_DASH = re.compile(r"[^a-z0-9]+") def make_url_friendly(text): text = text.lower() text = CHARS_TO_REMOVE.sub('', text) text = CHARS_TO_DASH.sub('-', text) return text.strip("-") business = Business()business.name = request.POST["name"]business.url = "/biz/" + make_url_friendly(business.name) business.date_created = datetime.datetime.utcnow() business.save_to_database()我们来看一个读写cookie的函数：
var max_results;var cookies = document.cookie.split(';');for (var i = 0; i < cookies.length; i++) { var c = cookies[i]; c = c.replace(/^[ ]+/, ''); // remove leading spaces if (c.indexOf("max_results=") === 0) max_results = Number(c.substring(12, c.length));}这段代码实在太丑了，理想的接口应该是这样的：
set_cookie(name, value, days_to_expire);delete_cookie(name);
对于并不理想的接口，你永远可以用自己的函数做封装，让接口更好用。
ser_info = { "username": "...", "password": "..." }user_str = json.dumps(user_info)cipher = Cipher("aes_128_cbc", key=PRIVATE_KEY, init_vector=INIT_VECTOR, op=ENCODE)encrypted_bytes = cipher.update(user_str)encrypted_bytes += cipher.final() # flush out the current 128 bit blockurl = "http://example.com/?user_info=" + base64.urlsafe_b64encode(encrypted_bytes)...虽然终极目的是拼接用户信息的字符，但是代码大部分做的事情是解析python的object，所以：
def url_safe_encrypt(obj): obj_str = json.dumps(obj) cipher = Cipher("aes_128_cbc", key=PRIVATE_KEY, init_vector=INIT_VECTOR, op=ENCODE) encrypted_bytes = cipher.update(obj_str) encrypted_bytes += cipher.final() # flush out the current 128 bit block return base64.urlsafe_b64encode(encrypted_bytes)这样在其他地方也可以调用：
user_info = { "username": "...", "password": "..." }url = "http://example.com/?user_info=" + url_safe_encrypt(user_info)分离子函数是好习惯，但是也要适度，过度的分离成多个小函数，也会让查找变得困难。
代码应该是一次只完成一个任务
var place = location_info["LocalityName"]; // e.g. "Santa Monica"if (!place) { place = location_info["SubAdministrativeAreaName"]; // e.g. "Los Angeles"}if (!place) { place = location_info["AdministrativeAreaName"]; // e.g. "California"}if (!place) { place = "Middle-of-Nowhere";}if (location_info["CountryName"]) { place += ", " + location_info["CountryName"]; // e.g. "USA"} else { place += ", Planet Earth";} return place;这是一个用来拼地名的函数，有很多的条件判断，读起来非常吃力，有没有办法拆解任务呢？
var town = location_info["LocalityName"]; // e.g. "Santa Monica"var city = location_info["SubAdministrativeAreaName"]; // e.g. "Los Angeles"var state = location_info["AdministrativeAreaName"]; // e.g. "CA"var country = location_info["CountryName"]; // e.g. "USA"
先拆解第一个任务，将各变量分别保存，这样在后面使用中不需要去记忆那些繁长的key值了，第二个任务，解决地址拼接的后半部分：
// Start with the default, and keep overwriting with the most specific value. var second_half = "Planet Earth";if (country) { second_half = country; }if (state && country === "USA") { second_half = state; }再来解决前半部分：
var first_half = "Middle-of-Nowhere";if (state && country !== "USA") { first_half = state; }if (city) { first_half = city;}if (town) { first_half = town; }大功告成：
return first_half + ", " + second_half;
如果注意到有USA这个变量的判断的话，也可以这样写：
var first_half, second_half;if (country === "USA") { first_half = town || city || "Middle-of-Nowhere"; second_half = state || "USA";} else { first_half = town || city || state || "Middle-of-Nowhere"; second_half = country || "Planet Earth";}return first_half + ", " + second_half;要把一个复杂的东西解释给别人，一些细节很容易就让人产生迷惑，所以想象把你的代码用平实的语言解释给别人听，别人是否能懂，有一些准则可以帮助你让代码更清晰：
用最平实的语言描述代码的目的，就像给读者讲述一样
注意描述中关键的字词
让你的代码符合你的描述
下面这段代码用来校验用户的权限：
$is_admin = is_admin_request();if ($document) { if (!$is_admin && ($document['username'] != $_SESSION['username'])) { return not_authorized(); }} else { if (!$is_admin) { return not_authorized(); } }// continue rendering the page ...这一段代码不长，里面的逻辑嵌套倒是复杂，参考前面章节所述，嵌套太多非常影响阅读理解，将这个逻辑用语言描述就是：
有两种情况有权限：1、你是管理员(admin)2、你拥有这个文档否则就没有权限
根据描述来写代码：
if (is_admin_request()) { // authorized} elseif ($document && ($document['username'] == $_SESSION['username'])) { // authorized} else { return not_authorized();}// continue rendering the page ...以上就是“web开发中怎么编写可读代码”这篇文章的所有内容，感谢各位的阅读！相信大家阅读完这篇文章都有很大的收获，小编每天都会为大家更新不同的知识，如果还想学习更多的知识，请关注亿速云行业资讯频道。
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