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<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="Link to this heading"></a></h1>
<p>Functions for number conversion and formatted string output.</p>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyOS_snprintf">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_snprintf</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">str</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">size</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">format</span></span>, <span class="p"><span class="pre">...</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_snprintf" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><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"><a class="manpage reference external" href="https://manpages.debian.org/snprintf(3)">snprintf(3)</a></em>.</p>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyOS_vsnprintf">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_vsnprintf</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">str</span></span>, <span class="n"><span class="pre">size_t</span></span><span class="w"> </span><span class="n"><span class="pre">size</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">format</span></span>, <span class="n"><span class="pre">va_list</span></span><span class="w"> </span><span class="n"><span class="pre">va</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_vsnprintf" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><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"><a class="manpage reference external" href="https://manpages.debian.org/vsnprintf(3)">vsnprintf(3)</a></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 <code class="docutils literal notranslate"><span class="pre">str[size-1]</span></code> 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">&gt;</span> <span class="pre">0</span></code>, <code class="docutils literal notranslate"><span class="pre">format</span> <span class="pre">!=</span> <span class="pre">NULL</span></code>
and <code class="docutils literal notranslate"><span class="pre">size</span> <span class="pre">&lt;</span> <span class="pre">INT_MAX</span></code>. Note that this means there is no equivalent to the C99
<code class="docutils literal notranslate"><span class="pre">n</span> <span class="pre">=</span> <span class="pre">snprintf(NULL,</span> <span class="pre">0,</span> <span class="pre">...)</span></code> which would determine the necessary buffer size.</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">&lt;=</span> <span class="pre">rv</span> <span class="pre">&lt;</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
<code class="docutils literal notranslate"><span class="pre">str[rv]</span></code>).</p></li>
<li><p>When <code class="docutils literal notranslate"><span class="pre">rv</span> <span class="pre">&gt;=</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. <code class="docutils literal notranslate"><span class="pre">str[size-1]</span></code> 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">&lt;</span> <span class="pre">0</span></code>, “something bad happened.” <code class="docutils literal notranslate"><span class="pre">str[size-1]</span></code> 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="c function">
<dt class="sig sig-object c" id="c.PyOS_strtoul">
<span class="kt"><span class="pre">unsigned</span></span><span class="w"> </span><span class="kt"><span class="pre">long</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_strtoul</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">str</span></span>, <span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ptr</span></span>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">base</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_strtoul" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Convert the initial part of the string in <code class="docutils literal notranslate"><span class="pre">str</span></code> to an <span class="c-expr sig sig-inline c"><span class="kt">unsigned</span><span class="w"> </span><span class="kt">long</span></span> value according to the given <code class="docutils literal notranslate"><span class="pre">base</span></code>, which must be between <code class="docutils literal notranslate"><span class="pre">2</span></code> and
<code class="docutils literal notranslate"><span class="pre">36</span></code> inclusive, or be the special value <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p>
<p>Leading white space and case of characters are ignored. If <code class="docutils literal notranslate"><span class="pre">base</span></code> is zero
it looks for a leading <code class="docutils literal notranslate"><span class="pre">0b</span></code>, <code class="docutils literal notranslate"><span class="pre">0o</span></code> or <code class="docutils literal notranslate"><span class="pre">0x</span></code> to tell which base. If
these are absent it defaults to <code class="docutils literal notranslate"><span class="pre">10</span></code>. Base must be 0 or between 2 and 36
(inclusive). If <code class="docutils literal notranslate"><span class="pre">ptr</span></code> is non-<code class="docutils literal notranslate"><span class="pre">NULL</span></code> it will contain a pointer to the
end of the scan.</p>
<p>If the converted value falls out of range of corresponding return type,
range error occurs (<code class="xref c c-data docutils literal notranslate"><span class="pre">errno</span></code> is set to <code class="xref c c-macro docutils literal notranslate"><span class="pre">ERANGE</span></code>) and
<code class="xref c c-macro docutils literal notranslate"><span class="pre">ULONG_MAX</span></code> is returned. If no conversion can be performed, <code class="docutils literal notranslate"><span class="pre">0</span></code>
is returned.</p>
<p>See also the Unix man page <em class="manpage"><a class="manpage reference external" href="https://manpages.debian.org/strtoul(3)">strtoul(3)</a></em>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.2.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyOS_strtol">
<span class="kt"><span class="pre">long</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_strtol</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">str</span></span>, <span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ptr</span></span>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">base</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_strtol" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Convert the initial part of the string in <code class="docutils literal notranslate"><span class="pre">str</span></code> to an <span class="c-expr sig sig-inline c"><span class="kt">long</span></span> value
according to the given <code class="docutils literal notranslate"><span class="pre">base</span></code>, which must be between <code class="docutils literal notranslate"><span class="pre">2</span></code> and <code class="docutils literal notranslate"><span class="pre">36</span></code>
inclusive, or be the special value <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p>
<p>Same as <a class="reference internal" href="#c.PyOS_strtoul" title="PyOS_strtoul"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyOS_strtoul()</span></code></a>, but return a <span class="c-expr sig sig-inline c"><span class="kt">long</span></span> value instead
and <code class="xref c c-macro docutils literal notranslate"><span class="pre">LONG_MAX</span></code> on overflows.</p>
<p>See also the Unix man page <em class="manpage"><a class="manpage reference external" href="https://manpages.debian.org/strtol(3)">strtol(3)</a></em>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.2.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyOS_string_to_double">
<span class="kt"><span class="pre">double</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_string_to_double</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">s</span></span>, <span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">endptr</span></span>, <a class="reference internal" href="structures.html#c.PyObject" title="PyObject"><span class="n"><span class="pre">PyObject</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">overflow_exception</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_string_to_double" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Convert a string <code class="docutils literal notranslate"><span class="pre">s</span></code> to a <span class="c-expr sig sig-inline c"><span class="kt">double</span></span>, 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">&quot;1e500&quot;</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">Added in version 3.1.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyOS_double_to_string">
<span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_double_to_string</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">double</span></span><span class="w"> </span><span class="n"><span class="pre">val</span></span>, <span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="n"><span class="pre">format_code</span></span>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">precision</span></span>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">flags</span></span>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">ptype</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_double_to_string" title="Link to this definition"></a><br /></dt>
<dd><em class="stableabi"> Part of the <a class="reference internal" href="stable.html#stable"><span class="std std-ref">Stable ABI</span></a>.</em><p>Convert a <span class="c-expr sig sig-inline c"><span class="kt">double</span></span> <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">Added in version 3.1.</span></p>
</div>
</dd></dl>
<dl class="c function">
<dt class="sig sig-object c" id="c.PyOS_stricmp">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_stricmp</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">s1</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">s2</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_stricmp" title="Link to this definition"></a><br /></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="c function">
<dt class="sig sig-object c" id="c.PyOS_strnicmp">
<span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">PyOS_strnicmp</span></span></span><span class="sig-paren">(</span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">s1</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="kt"><span class="pre">char</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">s2</span></span>, <a class="reference internal" href="intro.html#c.Py_ssize_t" title="Py_ssize_t"><span class="n"><span class="pre">Py_ssize_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">size</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.PyOS_strnicmp" title="Link to this definition"></a><br /></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>
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