Question

我正在编写一个Python函数，使用用户提交的凭据向URL发送GET请求，并获取返回的令牌供以后使用。

# Function for logging in and get a valid token
def getToken():
    while True: # Loop the cycle of logging in until valid token is received
        try:
            varUsername = raw_input("Enter your username: ")
            varPassword = getpass.getpass("Enter your password: ")
            reqAuthLogin = 'https://MY_URL?username=' + varUsername + '&password=' + varPassword # Send the login request
            varToken =  json.loads(urllib2.urlopen(reqAuthLogin).read())['Token'] # Attempt to parse the JSON response and read the Token, if possible
        except: # If credential is invalid and no token returned
            os.system('cls')
            print 'Invalid credentials. Please try again. \n'
        else: # I want this Try to exit the while loop if login is successful
            break

    os.system('cls')
    return varToken # Return the retrieved token at the end of this function

当用户名/密码组合不正确时，代码会抛出KeyError异常。我了解到Try-Else可以打破最内层的循环，在这种情况下应该是while循环。在我的设计中，我希望函数在发生异常时输出以下消息（意味着无效凭证）：

Invalid credentials. Please try again.

Enter your username:

如果登录成功，则代码应清除屏幕并返回获取的令牌。问题是，当这些代码不在Try而不是While时，这些代码运行良好。现在它在登录成功时输出：

Enter your username:

显然，即使没有异常发生，程序也不会执行Else分支。我是Python新手，请帮我确定导致此错误的原因。

编辑：感谢评论中的建议。我设置了几个断点，但断点显示即使我在try块的末尾插入一个break，程序先执行它然后直接返回＆＃34;而True＆＃34;声明。似乎中断没有成功退出循环。

Answer 1

为什么不添加在成功尝试结束时更改的bool？

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>jQuery UI Autocomplete - Combobox</title>
  <link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
     
<link href="https://www.tutorialspoint.com/bootstrap/css/bootstrap.min.css" rel="stylesheet">

  
  <style>
  .custom-combobox {
    position: relative;
    display: inline-block;
  }
  .custom-combobox-toggle {
    position: absolute;
    top: 0;
    bottom: 0;
    margin-left: -1px;
    padding: 0;
  }
  .custom-combobox-input {
    margin: 0;
    padding: 5px 10px;
  }
  </style>
  <script src="https://code.jquery.com/jquery-1.12.4.js"></script>
  <script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
    
        <script type="text/javascript">
        $.widget.bridge('uitooltip', $.ui.tooltip);
        $.widget.bridge('uibutton', $.ui.button);
    </script>
    
<script src="https://www.tutorialspoint.com/bootstrap/js/bootstrap.js"></script>
  

  <script>
  $( function() {
    $.widget( "custom.combobox", {
      _create: function() {
        this.wrapper = $( "<span>" )
          .addClass( "custom-combobox" )
          .insertAfter( this.element );
 
        this.element.hide();
        this._createAutocomplete();
        this._createShowAllButton();
      },
 
      _createAutocomplete: function() {
        var selected = this.element.children( ":selected" ),
          value = selected.val() ? selected.text() : "";
 
        this.input = $( "<input>" )
          .appendTo( this.wrapper )
          .val( value )
          .attr( "title", "" )
          .addClass( "custom-combobox-input ui-widget ui-widget-content ui-state-default ui-corner-left" )
          .autocomplete({
            delay: 0,
            minLength: 0,
            source: $.proxy( this, "_source" )
          })
          .uitooltip({
            classes: {
              "ui-tooltip": "ui-state-highlight"
            }
          });
 
        this._on( this.input, {
          autocompleteselect: function( event, ui ) {
            ui.item.option.selected = true;
            this._trigger( "select", event, {
              item: ui.item.option
            });
          },
 
          autocompletechange: "_removeIfInvalid"
        });
      },
 
      _createShowAllButton: function() {
        var input = this.input,
          wasOpen = false;
 
        $( "<a>" )
          .attr( "tabIndex", -1 )
          .attr( "title", "Show All Items" )
          .uitooltip()
          .appendTo( this.wrapper )
          .uibutton({
            icons: {
              primary: "ui-icon-triangle-1-s"
            },
            text: false
          })
          .removeClass( "ui-corner-all" )
          .addClass( "custom-combobox-toggle ui-corner-right" )
          .on( "mousedown", function() {
            wasOpen = input.autocomplete( "widget" ).is( ":visible" );
          })
          .on( "click", function() {
            input.trigger( "focus" );
 
            // Close if already visible
            if ( wasOpen ) {
              return;
            }
 
            // Pass empty string as value to search for, displaying all results
            input.autocomplete( "search", "" );
          });
      },
 
      _source: function( request, response ) {
        var matcher = new RegExp( $.ui.autocomplete.escapeRegex(request.term), "i" );
        response( this.element.children( "option" ).map(function() {
          var text = $( this ).text();
          if ( this.value && ( !request.term || matcher.test(text) ) )
            return {
              label: text,
              value: text,
              option: this
            };
        }) );
      },
 
      _removeIfInvalid: function( event, ui ) {
 
        // Selected an item, nothing to do
        if ( ui.item ) {
          return;
        }
 
        // Search for a match (case-insensitive)
        var value = this.input.val(),
          valueLowerCase = value.toLowerCase(),
          valid = false;
        this.element.children( "option" ).each(function() {
          if ( $( this ).text().toLowerCase() === valueLowerCase ) {
            this.selected = valid = true;
            return false;
          }
        });
 
        // Found a match, nothing to do
        if ( valid ) {
          return;
        }
 
        // Remove invalid value
        this.input
          .val( "" )
          .attr( "title", value + " didn't match any item" )
          .uitooltip( "open" );
        this.element.val( "" );
        this._delay(function() {
          this.input.tooltip( "close" ).attr( "title", "" );
        }, 2500 );
        this.input.autocomplete( "instance" ).term = "";
      },
 
      _destroy: function() {
        this.wrapper.remove();
        this.element.show();
      }
    });
 
    $( "#combobox" ).combobox();
    $( "#toggle" ).on( "click", function() {
      $( "#combobox" ).toggle();
    });
  } );
  </script>
</head>
<body>
 
<div class="ui-widget">
  <label>Your preferred programming language: </label>
  <select id="combobox">
    <option value="">Select one...</option>
    <option value="ActionScript">ActionScript</option>
    <option value="AppleScript">AppleScript</option>
    <option value="Asp">Asp</option>
    <option value="BASIC">BASIC</option>
    <option value="C">C</option>
    <option value="C++">C++</option>
    <option value="Clojure">Clojure</option>
    <option value="COBOL">COBOL</option>
    <option value="ColdFusion">ColdFusion</option>
    <option value="Erlang">Erlang</option>
    <option value="Fortran">Fortran</option>
    <option value="Groovy">Groovy</option>
    <option value="Haskell">Haskell</option>
    <option value="Java">Java</option>
    <option value="JavaScript">JavaScript</option>
    <option value="Lisp">Lisp</option>
    <option value="Perl">Perl</option>
    <option value="PHP">PHP</option>
    <option value="Python">Python</option>
    <option value="Ruby">Ruby</option>
    <option value="Scala">Scala</option>
    <option value="Scheme">Scheme</option>
  </select>
</div>
<button id="toggle">Show underlying select</button>
 
 
</body>
</html>

在Python中，如何从Try跳出While循环？

1 个答案: