kennethreitz/dive-into-python3
1
0
Fork 0
mirror of https://github.com/kennethreitz/dive-into-python3.git synced 2026-06-05 23:10:17 +00:00
Code Issues Packages Projects Releases Wiki Activity

STATUS=CLOSED dropped how-Python-datatypes-compare section and table because it's misleading and I don't care enough to fix it

Browse Source
This commit is contained in:
Mark Pilgrim
2009-05-15 13:27:35 -04:00
parent d7cceb643b
commit 3b8474a7bf
2 changed files with 10 additions and 55 deletions
Download Patch File Download Diff File Expand all files Collapse all files
dip2
+8 -31
View File
@@ -806,40 +806,17 @@ buildConnectionString Build a connection string from a dictionary Retur
<samp>buildConnectionString Build a connection string from a dictionary
Returns string.
</span></pre><h2 id="apihelper.optional">4.2. Using Optional and Named Arguments</h2>
<p>Python allows function arguments to have default values; if the function is called without the argument, the argument gets its default
value. Futhermore, arguments can be specified in any order by using named arguments. Stored procedures in SQL Server Transact/<abbr>SQL</abbr> can do this, so if you're a SQL Server scripting guru, you can skim this part.
<p>Here is an example of <code>info</code>, a function with two optional arguments:<pre><code>
def info(object, spacing=10, collapse=1):</pre><p><var>spacing</var> and <var>collapse</var> are optional, because they have default values defined. <var>object</var> is required, because it has no default value. If <code>info</code> is called with only one argument, <var>spacing</var> defaults to <code>10</code> and <var>collapse</var> defaults to <code>1</code>. If <code>info</code> is called with two arguments, <var>collapse</var> still defaults to <code>1</code>.
<p>Say you want to specify a value for <var>collapse</var> but want to accept the default value for <var>spacing</var>. In most languages, you would be out of luck, because you would need to call the function with three arguments. But in
Python, arguments can be specified by name, in any order.
<div class=example><h3>Example 4.4. Valid Calls of <code>info</code></h3><pre><code>
info(odbchelper) <span>&#x2460;</span>
info(odbchelper, 12) <span>&#x2461;</span>
info(odbchelper, collapse=0) <span>&#x2462;</span>
info(spacing=15, object=odbchelper) <span>&#x2463;</span></pre>
<ol>
<li>With only one argument, <var>spacing</var> gets its default value of <code>10</code> and <var>collapse</var> gets its default value of <code>1</code>.
<li>With two arguments, <var>collapse</var> gets its default value of <code>1</code>.
<li>Here you are naming the <var>collapse</var> argument explicitly and specifying its value. <var>spacing</var> still gets its default value of <code>10</code>.
<li>Even required arguments (like <var>object</var>, which has no default value) can be named, and named arguments can appear in any order.
<p>This looks totally whacked until you realize that arguments are simply a dictionary. The &#8220;normal&#8221; method of calling functions without argument names is actually just a shorthand where Python matches up the values with the argument names in the order they're specified in the function declaration. And most of the
time, you'll call functions the &#8220;normal&#8221; way, but you always have the additional flexibility if you need it.
<table id="tip.arguments" class=note border="0" summary="">
<td rowspan="2" align="center" valign="top" width="1%"><img src="images/note.png" alt="Note" title="" width="24" height="24"><td colspan="2" align="left" valign="top" width="99%">The only thing you need to do to call a function is specify a value (somehow) for each required argument; the manner and order
in which you do that is up to you.
<div class=itemizedlist>
<h3>Further Reading on Optional Arguments</h3>
<ul>
<li><a href="http://www.python.org/doc/current/tut/tut.html"><i class=citetitle>Python Tutorial</i></a> discusses exactly <a href="http://www.python.org/doc/current/tut/node6.html#SECTION006710000000000000000">when and how default arguments are evaluated</a>, which matters when the default value is a list or an expression with side effects.
</ul>
<h2 id="apihelper.builtin">4.3. Using <code>type</code>, <code>str</code>, <code>dir</code>, and Other Built-In Functions</h2>
<p>Python has a small set of extremely useful built-in functions. All other functions are partitioned off into modules. This was
actually a conscious design decision, to keep the core language from getting bloated like other scripting languages (cough
cough, Visual Basic).
(optional and named arguments stuff was here)
<h3>4.3.1. The <code>type</code> Function</h3>
<p>The <code>type</code> function returns the datatype of any arbitrary object. The possible types are listed in the <code>types</code> module. This is useful for helper functions that can handle several types of data.
<div class=example><h3 id="apihelper.type.intro">Example 4.5. Introducing <code>type</code></h3><pre class=screen><samp class=p>>>> </samp><kbd>type(1)</kbd> <span>&#x2460;</span>