<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="utf-8" />
<title>String conversion and formatting — Python 3.7.10 documentation</title>
<link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" />
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
<script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script>
<script type="text/javascript" src="../_static/jquery.js"></script>
<script type="text/javascript" src="../_static/underscore.js"></script>
<script type="text/javascript" src="../_static/doctools.js"></script>
<script type="text/javascript" src="../_static/language_data.js"></script>
<script type="text/javascript" src="../_static/sidebar.js"></script>
<link rel="search" type="application/opensearchdescription+xml"
title="Search within Python 3.7.10 documentation"
href="../_static/opensearch.xml"/>
<link rel="author" title="About these documents" href="../about.html" />
<link rel="index" title="Index" href="../genindex.html" />
<link rel="search" title="Search" href="../search.html" />
<link rel="copyright" title="Copyright" href="../copyright.html" />
<link rel="next" title="Reflection" href="reflection.html" />
<link rel="prev" title="Parsing arguments and building values" href="arg.html" />
<link rel="shortcut icon" type="image/png" href="../_static/py.png" />
<link rel="canonical" href="https://docs.python.org/3/c-api/conversion.html" />
<script type="text/javascript" src="../_static/copybutton.js"></script>
<style>
@media only screen {
table.full-width-table {
width: 100%;
}
}
</style>
</head><body>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="reflection.html" title="Reflection"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="arg.html" title="Parsing arguments and building values"
accesskey="P">previous</a> |</li>
<li><img src="../_static/py.png" alt=""
style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<a href="../index.html">3.7.10 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li>
<li class="nav-item nav-item-2"><a href="utilities.html" accesskey="U">Utilities</a> »</li>
<li class="right">
<div class="inline-search" style="display: none" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('.inline-search').show(0);</script>
|
</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<div class="section" id="string-conversion-and-formatting">
<span id="string-conversion"></span><h1>String conversion and formatting<a class="headerlink" href="#string-conversion-and-formatting" title="Permalink to this headline">¶</a></h1>
<p>Functions for number conversion and formatted string output.</p>
<dl class="function">
<dt id="c.PyOS_snprintf">
int <code class="sig-name descname">PyOS_snprintf</code><span class="sig-paren">(</span>char<em> *str</em>, size_t<em> size</em>, const char<em> *format</em>, ...<span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_snprintf" title="Permalink to this definition">¶</a></dt>
<dd><p>Output not more than <em>size</em> bytes to <em>str</em> according to the format string
<em>format</em> and the extra arguments. See the Unix man page <em class="manpage">snprintf(2)</em>.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyOS_vsnprintf">
int <code class="sig-name descname">PyOS_vsnprintf</code><span class="sig-paren">(</span>char<em> *str</em>, size_t<em> size</em>, const char<em> *format</em>, va_list<em> va</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_vsnprintf" title="Permalink to this definition">¶</a></dt>
<dd><p>Output not more than <em>size</em> bytes to <em>str</em> according to the format string
<em>format</em> and the variable argument list <em>va</em>. Unix man page
<em class="manpage">vsnprintf(2)</em>.</p>
</dd></dl>
<p><a class="reference internal" href="#c.PyOS_snprintf" title="PyOS_snprintf"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_snprintf()</span></code></a> and <a class="reference internal" href="#c.PyOS_vsnprintf" title="PyOS_vsnprintf"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_vsnprintf()</span></code></a> wrap the Standard C library
functions <code class="xref c c-func docutils literal notranslate"><span class="pre">snprintf()</span></code> and <code class="xref c c-func docutils literal notranslate"><span class="pre">vsnprintf()</span></code>. Their purpose is to
guarantee consistent behavior in corner cases, which the Standard C functions do
not.</p>
<p>The wrappers ensure that <em>str*[*size</em>-1] is always <code class="docutils literal notranslate"><span class="pre">'\0'</span></code> upon return. They
never write more than <em>size</em> bytes (including the trailing <code class="docutils literal notranslate"><span class="pre">'\0'</span></code>) into str.
Both functions require that <code class="docutils literal notranslate"><span class="pre">str</span> <span class="pre">!=</span> <span class="pre">NULL</span></code>, <code class="docutils literal notranslate"><span class="pre">size</span> <span class="pre">></span> <span class="pre">0</span></code> and <code class="docutils literal notranslate"><span class="pre">format</span> <span class="pre">!=</span>
<span class="pre">NULL</span></code>.</p>
<p>If the platform doesn’t have <code class="xref c c-func docutils literal notranslate"><span class="pre">vsnprintf()</span></code> and the buffer size needed to
avoid truncation exceeds <em>size</em> by more than 512 bytes, Python aborts with a
<a class="reference internal" href="sys.html#c.Py_FatalError" title="Py_FatalError"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_FatalError()</span></code></a>.</p>
<p>The return value (<em>rv</em>) for these functions should be interpreted as follows:</p>
<ul class="simple">
<li><p>When <code class="docutils literal notranslate"><span class="pre">0</span> <span class="pre"><=</span> <span class="pre">rv</span> <span class="pre"><</span> <span class="pre">size</span></code>, the output conversion was successful and <em>rv</em>
characters were written to <em>str</em> (excluding the trailing <code class="docutils literal notranslate"><span class="pre">'\0'</span></code> byte at
<em>str*[*rv</em>]).</p></li>
<li><p>When <code class="docutils literal notranslate"><span class="pre">rv</span> <span class="pre">>=</span> <span class="pre">size</span></code>, the output conversion was truncated and a buffer with
<code class="docutils literal notranslate"><span class="pre">rv</span> <span class="pre">+</span> <span class="pre">1</span></code> bytes would have been needed to succeed. <em>str*[*size</em>-1] is <code class="docutils literal notranslate"><span class="pre">'\0'</span></code>
in this case.</p></li>
<li><p>When <code class="docutils literal notranslate"><span class="pre">rv</span> <span class="pre"><</span> <span class="pre">0</span></code>, “something bad happened.” <em>str*[*size</em>-1] is <code class="docutils literal notranslate"><span class="pre">'\0'</span></code> in
this case too, but the rest of <em>str</em> is undefined. The exact cause of the error
depends on the underlying platform.</p></li>
</ul>
<p>The following functions provide locale-independent string to number conversions.</p>
<dl class="function">
<dt id="c.PyOS_string_to_double">
double <code class="sig-name descname">PyOS_string_to_double</code><span class="sig-paren">(</span>const char<em> *s</em>, char<em> **endptr</em>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *overflow_exception</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_string_to_double" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a string <code class="docutils literal notranslate"><span class="pre">s</span></code> to a <code class="xref c c-type docutils literal notranslate"><span class="pre">double</span></code>, raising a Python
exception on failure. The set of accepted strings corresponds to
the set of strings accepted by Python’s <a class="reference internal" href="../library/functions.html#float" title="float"><code class="xref py py-func docutils literal notranslate"><span class="pre">float()</span></code></a> constructor,
except that <code class="docutils literal notranslate"><span class="pre">s</span></code> must not have leading or trailing whitespace.
The conversion is independent of the current locale.</p>
<p>If <code class="docutils literal notranslate"><span class="pre">endptr</span></code> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, convert the whole string. Raise
<a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> and return <code class="docutils literal notranslate"><span class="pre">-1.0</span></code> if the string is not a valid
representation of a floating-point number.</p>
<p>If endptr is not <code class="docutils literal notranslate"><span class="pre">NULL</span></code>, convert as much of the string as
possible and set <code class="docutils literal notranslate"><span class="pre">*endptr</span></code> to point to the first unconverted
character. If no initial segment of the string is the valid
representation of a floating-point number, set <code class="docutils literal notranslate"><span class="pre">*endptr</span></code> to point
to the beginning of the string, raise ValueError, and return
<code class="docutils literal notranslate"><span class="pre">-1.0</span></code>.</p>
<p>If <code class="docutils literal notranslate"><span class="pre">s</span></code> represents a value that is too large to store in a float
(for example, <code class="docutils literal notranslate"><span class="pre">"1e500"</span></code> is such a string on many platforms) then
if <code class="docutils literal notranslate"><span class="pre">overflow_exception</span></code> is <code class="docutils literal notranslate"><span class="pre">NULL</span></code> return <code class="docutils literal notranslate"><span class="pre">Py_HUGE_VAL</span></code> (with
an appropriate sign) and don’t set any exception. Otherwise,
<code class="docutils literal notranslate"><span class="pre">overflow_exception</span></code> must point to a Python exception object;
raise that exception and return <code class="docutils literal notranslate"><span class="pre">-1.0</span></code>. In both cases, set
<code class="docutils literal notranslate"><span class="pre">*endptr</span></code> to point to the first character after the converted value.</p>
<p>If any other error occurs during the conversion (for example an
out-of-memory error), set the appropriate Python exception and
return <code class="docutils literal notranslate"><span class="pre">-1.0</span></code>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.1.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="c.PyOS_double_to_string">
char* <code class="sig-name descname">PyOS_double_to_string</code><span class="sig-paren">(</span>double<em> val</em>, char<em> format_code</em>, int<em> precision</em>, int<em> flags</em>, int<em> *ptype</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_double_to_string" title="Permalink to this definition">¶</a></dt>
<dd><p>Convert a <code class="xref c c-type docutils literal notranslate"><span class="pre">double</span></code> <em>val</em> to a string using supplied
<em>format_code</em>, <em>precision</em>, and <em>flags</em>.</p>
<p><em>format_code</em> must be one of <code class="docutils literal notranslate"><span class="pre">'e'</span></code>, <code class="docutils literal notranslate"><span class="pre">'E'</span></code>, <code class="docutils literal notranslate"><span class="pre">'f'</span></code>, <code class="docutils literal notranslate"><span class="pre">'F'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'g'</span></code>, <code class="docutils literal notranslate"><span class="pre">'G'</span></code> or <code class="docutils literal notranslate"><span class="pre">'r'</span></code>. For <code class="docutils literal notranslate"><span class="pre">'r'</span></code>, the supplied <em>precision</em>
must be 0 and is ignored. The <code class="docutils literal notranslate"><span class="pre">'r'</span></code> format code specifies the
standard <a class="reference internal" href="../library/functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> format.</p>
<p><em>flags</em> can be zero or more of the values <code class="docutils literal notranslate"><span class="pre">Py_DTSF_SIGN</span></code>,
<code class="docutils literal notranslate"><span class="pre">Py_DTSF_ADD_DOT_0</span></code>, or <code class="docutils literal notranslate"><span class="pre">Py_DTSF_ALT</span></code>, or-ed together:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">Py_DTSF_SIGN</span></code> means to always precede the returned string with a sign
character, even if <em>val</em> is non-negative.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">Py_DTSF_ADD_DOT_0</span></code> means to ensure that the returned string will not look
like an integer.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">Py_DTSF_ALT</span></code> means to apply “alternate” formatting rules. See the
documentation for the <a class="reference internal" href="#c.PyOS_snprintf" title="PyOS_snprintf"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_snprintf()</span></code></a> <code class="docutils literal notranslate"><span class="pre">'#'</span></code> specifier for
details.</p></li>
</ul>
<p>If <em>ptype</em> is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code>, then the value it points to will be set to one of
<code class="docutils literal notranslate"><span class="pre">Py_DTST_FINITE</span></code>, <code class="docutils literal notranslate"><span class="pre">Py_DTST_INFINITE</span></code>, or <code class="docutils literal notranslate"><span class="pre">Py_DTST_NAN</span></code>, signifying that
<em>val</em> is a finite number, an infinite number, or not a number, respectively.</p>
<p>The return value is a pointer to <em>buffer</em> with the converted string or
<code class="docutils literal notranslate"><span class="pre">NULL</span></code> if the conversion failed. The caller is responsible for freeing the
returned string by calling <a class="reference internal" href="memory.html#c.PyMem_Free" title="PyMem_Free"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMem_Free()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.1.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="c.PyOS_stricmp">
int <code class="sig-name descname">PyOS_stricmp</code><span class="sig-paren">(</span>const char<em> *s1</em>, const char<em> *s2</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_stricmp" title="Permalink to this definition">¶</a></dt>
<dd><p>Case insensitive comparison of strings. The function works almost
identically to <code class="xref c c-func docutils literal notranslate"><span class="pre">strcmp()</span></code> except that it ignores the case.</p>
</dd></dl>
<dl class="function">
<dt id="c.PyOS_strnicmp">
int <code class="sig-name descname">PyOS_strnicmp</code><span class="sig-paren">(</span>const char<em> *s1</em>, const char<em> *s2</em>, Py_ssize_t <em> size</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_strnicmp" title="Permalink to this definition">¶</a></dt>
<dd><p>Case insensitive comparison of strings. The function works almost
identically to <code class="xref c c-func docutils literal notranslate"><span class="pre">strncmp()</span></code> except that it ignores the case.</p>
</dd></dl>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h4>Previous topic</h4>
<p class="topless"><a href="arg.html"
title="previous chapter">Parsing arguments and building values</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="reflection.html"
title="next chapter">Reflection</a></p>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">Report a Bug</a></li>
<li>
<a href="https://github.com/python/cpython/blob/3.7/Doc/c-api/conversion.rst"
rel="nofollow">Show Source
</a>
</li>
</ul>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
>index</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python Module Index"
>modules</a> |</li>
<li class="right" >
<a href="reflection.html" title="Reflection"
>next</a> |</li>
<li class="right" >
<a href="arg.html" title="Parsing arguments and building values"
>previous</a> |</li>
<li><img src="../_static/py.png" alt=""
style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<a href="../index.html">3.7.10 Documentation</a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li>
<li class="nav-item nav-item-2"><a href="utilities.html" >Utilities</a> »</li>
<li class="right">
<div class="inline-search" style="display: none" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('.inline-search').show(0);</script>
|
</li>
</ul>
</div>
<div class="footer">
© <a href="../copyright.html">Copyright</a> 2001-2021, Python Software Foundation.
<br />
The Python Software Foundation is a non-profit corporation.
<a href="https://www.python.org/psf/donations/">Please donate.</a>
<br />
Last updated on Feb 26, 2021.
<a href="../bugs.html">Found a bug</a>?
<br />
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.3.1.
</div>
</body>
</html>
