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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>String conversion and formatting — Python 3.6.7 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/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 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> </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">3.6.7 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="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="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 <em>Py_FatalError</em>.</p> <p>The return value (<em>rv</em>) for these functions should be interpreted as follows:</p> <ul class="simple"> <li>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>]).</li> <li>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.</li> <li>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.</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="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 ValueError 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">New in version 3.1.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyOS_double_to_string"> char* <code class="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 <em>Py_DTSF_SIGN</em>, <em>Py_DTSF_ADD_DOT_0</em>, or <em>Py_DTSF_ALT</em>, or-ed together:</p> <ul class="simple"> <li><em>Py_DTSF_SIGN</em> means to always precede the returned string with a sign character, even if <em>val</em> is non-negative.</li> <li><em>Py_DTSF_ADD_DOT_0</em> means to ensure that the returned string will not look like an integer.</li> <li><em>Py_DTSF_ALT</em> 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.</li> </ul> <p>If <em>ptype</em> is non-NULL, then the value it points to will be set to one of <em>Py_DTST_FINITE</em>, <em>Py_DTST_INFINITE</em>, or <em>Py_DTST_NAN</em>, 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 <em>NULL</em> 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">New in version 3.1.</span></p> </div> </dd></dl> <dl class="function"> <dt id="c.PyOS_stricmp"> int <code class="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="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/3.6/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">3.6.7 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> 2001-2023, 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 Dec 18, 2023. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.7.6. </div> </body> </html>