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<title>3.11.4 The interpreter stack </title>
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<H2><A NAME="SECTION0051140000000000000000"><!--x--></A><A NAME="inspect-stack"><!--z--></A>
<BR>
3.11.4 The interpreter stack
</H2>
<P>
When the following functions return ``frame records,'' each record
is a tuple of six items: the frame object, the filename,
the line number of the current line, the function name, a list of
lines of context from the source code, and the index of the current
line within that list.
<P>
<div class="warning"><b class="label">Warning:</b>
Keeping references to frame objects, as found in
the first element of the frame records these functions return, can
cause your program to create reference cycles. Once a reference cycle
has been created, the lifespan of all objects which can be accessed
from the objects which form the cycle can become much longer even if
Python's optional cycle detector is enabled. If such cycles must be
created, it is important to ensure they are explicitly broken to avoid
the delayed destruction of objects and increased memory consumption
which occurs.
<P>
Though the cycle detector will catch these, destruction of the frames
(and local variables) can be made deterministic by removing the cycle
in a <tt class="keyword">finally</tt> clause. This is also important if the cycle
detector was disabled when Python was compiled or using
<tt class="function"><tt class="module"><a href="module-gc.html">gc</a></tt>.disable()</tt>. For example:
<P>
<div class="verbatim"><pre>
def handle_stackframe_without_leak():
frame = inspect.currentframe()
try:
# do something with the frame
finally:
del frame
</pre></div>
</div>
<P>
The optional <var>context</var> argument supported by most of these
functions specifies the number of lines of context to return, which
are centered around the current line.
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-589' class="function">getframeinfo</tt></b>(</nobr></td>
<td><var>frame</var><big>[</big><var>, context</var><big>]</big>)</td></tr></table></dt>
<dd>
Get information about a frame or traceback object. A 5-tuple
is returned, the last five elements of the frame's frame record.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-590' class="function">getouterframes</tt></b>(</nobr></td>
<td><var>frame</var><big>[</big><var>, context</var><big>]</big>)</td></tr></table></dt>
<dd>
Get a list of frame records for a frame and all outer frames. These
frames represent the calls that lead to the creation of <var>frame</var>.
The first entry in the returned list represents <var>frame</var>; the
last entry represents the outermost call on <var>frame</var>'s stack.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-591' class="function">getinnerframes</tt></b>(</nobr></td>
<td><var>traceback</var><big>[</big><var>, context</var><big>]</big>)</td></tr></table></dt>
<dd>
Get a list of frame records for a traceback's frame and all inner
frames. These frames represent calls made as a consequence of
<var>frame</var>. The first entry in the list represents
<var>traceback</var>; the last entry represents where the exception was
raised.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-592' class="function">currentframe</tt></b>(</nobr></td>
<td>)</td></tr></table></dt>
<dd>
Return the frame object for the caller's stack frame.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-593' class="function">stack</tt></b>(</nobr></td>
<td><big>[</big><var>context</var><big>]</big>)</td></tr></table></dt>
<dd>
Return a list of frame records for the caller's stack. The first
entry in the returned list represents the caller; the last entry
represents the outermost call on the stack.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-594' class="function">trace</tt></b>(</nobr></td>
<td><big>[</big><var>context</var><big>]</big>)</td></tr></table></dt>
<dd>
Return a list of frame records for the stack between the current
frame and the frame in which an exception currently being handled
was raised in. The first entry in the list represents the caller;
the last entry represents where the exception was raised.
</dl>
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<span class="release-info">Release 2.3.4, documentation updated on May 20, 2004.</span>
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