Allow better custom type error messages using ArgumentTypeError.

6 files changed, 43 insertions, 6 deletions

diff --git a/NEWS.txt b/NEWS.txt
index 647bbef..099b916 100644
--- a/NEWS.txt
+++ b/NEWS.txt
@@ -2,6 +2,7 @@ What's New in argparse 1.1
 ==========================
 
 - Issue #22: Support more customization of version arguments.
+- Issue #34: Allow better custom type error messages using ArgumentTypeError.
 - Issue #36: Get "from argparse import *" working.
 - Issue #37: Stop treating two character alphanumeric flags as numbers.
 - Issue #38: Better error messages when 'dest' occurs twice for positional arguments.
diff --git a/argparse.py b/argparse.py
index 4f3edfb..bd03f29 100644
--- a/argparse.py
+++ b/argparse.py
@@ -722,6 +722,12 @@ class ArgumentError(Exception):
         return format % dict(message=self.message,
                              argument_name=self.argument_name)
 
+
+class ArgumentTypeError(Exception):
+    """An error from trying to convert a command line string to a type."""
+    pass
+
+
 # ==============
 # Action classes
 # ==============
@@ -2191,7 +2197,13 @@ class ArgumentParser(_AttributeHolder, _ActionsContainer):
         try:
             result = type_func(arg_string)
 
-        # TypeErrors or ValueErrors indicate errors
+        # ArgumentTypeErrors indicate errors
+        except ArgumentTypeError:
+            name = getattr(action.type, '__name__', repr(action.type))
+            msg = str(_sys.exc_info()[1])
+            raise ArgumentError(action, msg)
+
+        # TypeErrors or ValueErrors also indicate errors
         except (TypeError, ValueError):
             name = getattr(action.type, '__name__', repr(action.type))
             msg = _('invalid %s value: %r')
diff --git a/doc/add_argument.html b/doc/add_argument.html
index c4e1d30..1d34a65 100644
--- a/doc/add_argument.html
+++ b/doc/add_argument.html
@@ -295,7 +295,8 @@
 <span class="gp">... </span>    <span class="n">value</span> <span class="o">=</span> <span class="nb">int</span><span class="p">(</span><span class="n">string</span><span class="p">)</span>
 <span class="gp">... </span>    <span class="n">sqrt</span> <span class="o">=</span> <span class="n">math</span><span class="o">.</span><span class="n">sqrt</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
 <span class="gp">... </span>    <span class="k">if</span> <span class="n">sqrt</span> <span class="o">!=</span> <span class="nb">int</span><span class="p">(</span><span class="n">sqrt</span><span class="p">):</span>
-<span class="gp">... </span>    <span class="k">raise</span> <span class="ne">TypeError</span><span class="p">()</span>
+<span class="gp">... </span>        <span class="n">msg</span> <span class="o">=</span> <span class="s">&quot;</span><span class="si">%r</span><span class="s"> is not a perfect square&quot;</span> <span class="o">%</span> <span class="n">string</span>
+<span class="gp">... </span>        <span class="k">raise</span> <span class="n">argparse</span><span class="o">.</span><span class="n">ArgumentTypeError</span><span class="p">(</span><span class="n">msg</span><span class="p">)</span>
 <span class="gp">... </span>    <span class="k">return</span> <span class="n">value</span>
 <span class="gp">...</span>
 <span class="gp">&gt;&gt;&gt; </span><span class="n">parser</span> <span class="o">=</span> <span class="n">argparse</span><span class="o">.</span><span class="n">ArgumentParser</span><span class="p">(</span><span class="n">prog</span><span class="o">=</span><span class="s">&#39;PROG&#39;</span><span class="p">)</span>
@@ -304,7 +305,7 @@
 <span class="go">Namespace(foo=9)</span>
 <span class="gp">&gt;&gt;&gt; </span><span class="n">parser</span><span class="o">.</span><span class="n">parse_args</span><span class="p">(</span><span class="s">&#39;7&#39;</span><span class="o">.</span><span class="n">split</span><span class="p">())</span>
 <span class="go">usage: PROG [-h] foo</span>
-<span class="go">PROG: error: argument foo: invalid perfect_square value: &#39;7&#39;</span>
+<span class="go">PROG: error: argument foo: &#39;7&#39; is not a perfect square</span>
 </pre></div>
 </div>
 <p>Note that if your type-checking function is just checking for a particular set of values, it may be more convenient to use the <a class="reference internal" href="#choices">choices</a> keyword argument:</p>
diff --git a/doc/searchindex.js b/doc/searchindex.js
index 0f82ba4..838a23f 100644
--- a/doc/searchindex.js
+++ b/doc/searchindex.js
@@ -1 +1 @@
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\ No newline at end of file
+Search.setIndex({desctypes:{"0":"method","1":"class"},terms:{all:[6,3,7,5,2],code:[0,7,6],partial:[8,7,2],messg:7,whatev:2,illustr:[7,5],global:6,four:5,prefix:[1,6,5],upgrad:[0,7],follow:[0,7,5,6,3],formatter_class:[8,6],whose:[5,6],typeerror:[],"const":[8,3,7,1,5],readabl:4,prefix_char:[8,7,6],program:[6,0,5,2,3],present:[7,1,2,5],sens:[5,6],worth:5,consum:[7,5],everi:3,string:[1,2,3,5,6,7],fals:[6,7,5,2],subcommand:[7,2],util:[8,0,4],parent_pars:6,default_:[],exact:7,implement:5,level:2,list:[1,2,3,5,6,7],"try":[7,6],item:[5,2],adjust:6,stderr:2,pleas:6,subparser_nam:2,bacon:1,dogmat:7,past:7,zero:[7,5],fyoyo:7,group1:2,pass:[1,2,4,5,6,7],append:5,compat:7,what:[3,7,1,6,5],abc:[7,5],sub:[8,7,2],neg:1,section:[6,7,5,2],advanc:7,brief:[6,5,2],current:[6,2],abbrevi:[8,1],version:[8,5,6],"new":[7,1,6,5],method:[0,1,2,3,5,6,7,8],told:5,deriv:[7,5],gener:[0,7,5,6,3],never:[7,6],here:[7,1],let:2,inher:1,path:7,along:1,infil:[4,5],modifi:2,sinc:7,interpret:5,convert:[3,4,7,1,5],produc:[7,5,2],convers:5,pick:1,action:[1,2,3,5,6,7,8],weird:6,commonli:5,control:6,regardless:6,extra:[1,2],appli:5,modul:[0,7,5,3],prefer:7,filenam:5,api:[8,0,7,5],txt:[0,5,6],select:[5,2],add_argument_group:2,from:[1,2,3,5,6,7],describ:[6,5,2],would:[7,5],frobbl:[5,2],regist:2,two:[6,3,1,2,5],few:[7,5,2],call:[0,1,2,3,5,6,7],add_help:[8,7,6,2],recommend:2,taken:[7,1,5],rawtexthelpformatt:6,type:[0,1,2,3,4,5,6,7,8],tell:[3,1],more:[0,1,3,5,6,7],sort:[3,5,6],parser_a:2,parser_b:2,notic:[7,1],warn:5,flag:[8,7,5],indic:[6,5,2],particular:[7,5,2],known:7,hold:[3,5],easiest:[7,5,2],must:[1,6,5],dictat:7,none:[4,7,1,6,5],word:6,dest:[1,2,3,5,7,8],work:[6,2],conceptu:2,remain:[3,7,5,2],itself:5,can:[0,1,2,3,4,5,6,7],def:[7,5,2],overrid:[7,6,2],traceback:6,prompt:1,puriti:7,give:[1,6],frabbl:3,share:[7,6],add_argu:[0,1,2,3,4,5,6,7,8],accept:[7,5,2],cautiou:1,want:[6,3,7,5,2],alwai:[6,5,2],multipl:[7,5,2],thing:5,rather:[1,6],anoth:[6,5,2],check_method:7,fooaction:[7,5],write:[0,7,6,3],how:[6,3,1,2,5],sever:[6,1,2],instead:[7,5,2],narg:[0,1,3,5,6,7,8],simpl:[0,7,5,3],updat:2,parser_abc:7,foo_pars:[7,6],overridden:6,mess:6,max:[3,1],after:[6,7,1,2,5],variant:2,invok:[6,3,7,5,2],befor:[5,6],wrong:1,okai:6,mai:[6,7,1,2,5],end:[7,5,2],associ:[5,2],xfoox:7,"0x013a2410":[],"short":[1,6,5],attempt:[7,1],practic:7,stdin:[4,5],explicit:5,correspond:[3,7],ambigu:1,caus:[5,6],callback:7,type_:[],maintain:[7,6],combin:[1,2],allow:[6,7,1,2,5],callabl:[7,5],origin:[7,6],least:[5,2],help:[0,1,2,3,5,6,7,8],over:[7,6],becaus:6,through:7,same:[7,5,6],hierarchi:7,metavar_:[],still:5,subparser2:2,subparser1:2,paramet:[7,5,6],perfect:5,style:1,interspers:7,group:[8,2],fit:6,better:[7,2],main:2,easier:1,them:[0,5,1,6,3],good:2,"return":[3,7,1,2,5],greater:6,thei:[7,1,6,5],python:[0,7,6,2],initi:[3,5],option_str:[7,5],now:[3,7],discuss:7,introduct:[0,3],choic:[1,2,3,5,7,8],allow_interspersed_arg:7,optionerror:7,name:[1,2,3,5,6,7,8],anyth:[7,5],choices_:[],separ:[1,2],easili:7,achiev:[1,6],mode:[4,7,5],each:[6,3,7,5,2],fulli:2,difficult:7,nbar:6,mean:[3,7,5,6],myprogram:6,replac:[7,6],idea:2,heavi:1,expect:[3,1,5],our:3,happen:7,beyond:[8,1],metavar:[0,1,3,5,7,8],special:[5,2],out:[0,4,5,6,3],variabl:7,accomplish:[1,6],referenc:6,space:6,foo_bar:5,newli:1,parser_xyz:7,perfect_squar:5,print:[1,2,3,5,6,7,8],factori:[4,5],math:5,common:[3,5,6],optionvalueerror:7,worthwhil:7,situat:[1,5],given:6,argv:[8,3,1,6],standard:7,mmm:1,reason:7,base:7,dictionari:7,care:[7,2],indent:6,could:[1,5],omit:5,refus:7,keep:6,fromfile_prefix_char:[8,6],turn:3,place:6,isn:[7,5],retain:6,const_:[],assign:1,first:[5,6],oper:5,rang:[3,1],directli:5,carri:3,onc:3,number:[6,7,1,2,5],restrict:5,instruct:3,alreadi:[7,1,6],construct:[7,6],wasn:5,open:[4,7,5,6],size:4,differ:[7,5,2],script:[3,2],top:2,sometim:[6,1,2],messag:[0,1,2,5,6,7],too:5,similarli:2,conveni:[7,5],"final":[],store:[3,5],monkei:7,option:[0,1,2,3,5,6,7,8],namespac:[1,2,3,4,5,6,7,8],copi:7,specifi:[0,1,2,3,5,6,7],pars:[0,1,2,3,5,7,8],store_tru:[3,7,1,2,5],exactli:[3,1,6],than:[6,7,1,2,5],format_usag:2,wide:6,kind:2,setattr:[7,5],whenev:[1,5],provid:[0,7,1,2,5],remov:6,charact:[7,1,6,5],str:5,were:[5,6],posit:[0,1,2,3,5,6,7],seri:[3,5],sai:7,abov:[6,0,1,2,3],"0x013a2380":[],group2:2,argument:[0,1,2,3,4,5,6,7,8],dash:7,add_pars:[7,2],manner:[3,7],have:[4,7,1,6,5],"__main__":[0,3],need:[6,7,5,2],seem:7,squar:5,equival:6,inform:[6,3,7,5,2],self:[7,5],append_const:5,also:[6,1,2,5],builtin:5,exampl:[0,1,2,3,5,6],take:[1,2,3,5,6,7],which:[6,7,1,2,5],singl:[1,2,3,5,6,7],uppercas:5,begin:[3,1],sure:[7,5,2],though:5,buffer:4,previou:[7,1],most:[6,3,7,5,2],regular:2,pair:[7,6],choos:[7,5],"class":[4,7,1,6,5],appear:2,don:[7,1,5],gather:5,request:[4,5,2],doe:[6,7,5,2],declar:7,determin:[1,2,3,5,6,7],occasion:6,sum:[0,1,3],"0x00b8fb18":[],parser_bar:2,show:[6,0,7,5,2],text:6,filetyp:[8,0,4,5],syntax:[8,7,1],particularli:[7,6,2],hack:7,find:[3,1,2],onli:[6,7,1,2,5],textual:6,parse_known_arg:2,just:[5,2],pretti:3,"true":[1,2,3,5,6,7],parser_foo: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\ No newline at end of file
diff --git a/doc/source/add_argument.rst b/doc/source/add_argument.rst
index 4bdc43e..e72df5b 100644
--- a/doc/source/add_argument.rst
+++ b/doc/source/add_argument.rst
@@ -244,7 +244,8 @@ If you need to do some special type-checking or type-conversions, you can provid
   ...     value = int(string)
   ...     sqrt = math.sqrt(value)
   ...     if sqrt != int(sqrt):
-  ...     raise TypeError()
+  ...         msg = "%r is not a perfect square" % string
+  ...         raise argparse.ArgumentTypeError(msg)
   ...     return value
   ...    
   >>> parser = argparse.ArgumentParser(prog='PROG')
@@ -253,7 +254,7 @@ If you need to do some special type-checking or type-conversions, you can provid
   Namespace(foo=9)
   >>> parser.parse_args('7'.split())
   usage: PROG [-h] foo
-  PROG: error: argument foo: invalid perfect_square value: '7'
+  PROG: error: argument foo: '7' is not a perfect square
 
 Note that if your type-checking function is just checking for a particular set of values, it may be more convenient to use the choices_ keyword argument::
 
diff --git a/test/test_argparse.py b/test/test_argparse.py
index 4835b1d..c9ec289 100644
--- a/test/test_argparse.py
+++ b/test/test_argparse.py
@@ -3985,6 +3985,28 @@ class TestArgumentError(TestCase):
         error = argparse.ArgumentError(None, msg)
         self.failUnlessEqual(str(error), msg)
 
+# =======================
+# ArgumentTypeError tests
+# =======================
+
+class TestArgumentError(TestCase):
+
+    def test_argument_type_error(self):
+
+        def spam(string):
+            raise argparse.ArgumentTypeError('spam!')
+
+        parser = ErrorRaisingArgumentParser(prog='PROG', add_help=False)
+        parser.add_argument('x', type=spam)
+        try:
+            parser.parse_args(['XXX'])
+        except ArgumentParserError:
+            expected = 'usage: PROG x\nPROG: error: argument x: spam!\n'
+            msg = str(sys.exc_info()[1])
+            self.failUnlessEqual(expected, msg)
+        else:
+            self.fail()
+
 # ======================
 # parse_known_args tests
 # ======================