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Package netcdftime ::
<a href="netcdftime.netcdftime-module.html">Module netcdftime</a> ::
Class utime
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<!-- ==================== CLASS DESCRIPTION ==================== -->
<h1 class="epydoc">Class utime</h1><p class="nomargin-top"><span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime">source code</a></span></p>
<p>Performs conversions of netCDF time coordinate data to/from datetime
objects.</p>
<p>To initialize: <code>t =
utime(unit_string,calendar='standard')</code></p>
<p>where</p>
<p><b><code>unit_string</code></b> is a string of the form
<code>'time-units since <time-origin>'</code> defining the time
units.</p>
<p>Valid time-units are days, hours, minutes and seconds (the singular
forms are also accepted). An example unit_string would be <code>'hours
since 0001-01-01 00:00:00'</code>.</p>
<p>The <b><code>calendar</code></b> keyword describes the calendar used
in the time calculations. All the values currently defined in the <a
href="http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.1/cf-conventions.html#time-coordinate"
target="_top">CF metadata convention</a> are accepted. The default is
<code>'standard'</code>, which corresponds to the mixed Gregorian/Julian
calendar used by the <code>udunits library</code>. Valid calendars
are:</p>
<p><code>'gregorian'</code> or <code>'standard'</code> (default):</p>
<p>Mixed Gregorian/Julian calendar as defined by udunits.</p>
<p><code>'proleptic_gregorian'</code>:</p>
<p>A Gregorian calendar extended to dates before 1582-10-15. That is, a
year is a leap year if either (i) it is divisible by 4 but not by 100 or
(ii) it is divisible by 400.</p>
<p><code>'noleap'</code> or <code>'365_day'</code>:</p>
<p>Gregorian calendar without leap years, i.e., all years are 365 days
long. all_leap or 366_day Gregorian calendar with every year being a leap
year, i.e., all years are 366 days long.</p>
<p><code>'360_day'</code>:</p>
<p>All years are 360 days divided into 30 day months.</p>
<p><code>'julian'</code>:</p>
<p>Proleptic Julian calendar, extended to dates after 1582-10-5. A year
is a leap year if it is divisible by 4.</p>
<p>The <code><a href="netcdftime.netcdftime.utime-class.html#num2date"
class="link">num2date</a></code> and <code><a
href="netcdftime.netcdftime.utime-class.html#date2num"
class="link">date2num</a></code> class methods can used to convert
datetime instances to/from the specified time units using the specified
calendar.</p>
<p>The datetime instances returned by <code>num2date</code> are 'real'
python datetime objects if the date falls in the Gregorian calendar (i.e.
<code>calendar='proleptic_gregorian', 'standard'</code> or
<code>'gregorian'</code> and the date is after 1582-10-15). Otherwise,
they are 'phony' datetime objects which are actually instances of
<code><a href="netcdftime.netcdftime.datetime-class.html"
class="link">netcdftime.datetime</a></code>. This is because the python
datetime module cannot handle the weird dates in some calendars (such as
<code>'360_day'</code> and <code>'all_leap'</code>) which don't exist in
any real world calendar.</p>
<p>Example usage:</p>
<pre class="py-doctest">
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> netcdftime <span class="py-keyword">import</span> utime
<span class="py-prompt">>>> </span><span class="py-keyword">from</span> datetime <span class="py-keyword">import</span> datetime
<span class="py-prompt">>>> </span>cdftime = utime(<span class="py-string">'hours since 0001-01-01 00:00:00'</span>)
<span class="py-prompt">>>> </span>date = datetime.now()
<span class="py-prompt">>>> </span><span class="py-keyword">print</span> date
<span class="py-output">2006-03-17 16:04:02.561678</span>
<span class="py-output"></span><span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>t = cdftime.date2num(date)
<span class="py-prompt">>>> </span><span class="py-keyword">print</span> t
<span class="py-output">17577328.0672</span>
<span class="py-output"></span><span class="py-prompt">>>></span>
<span class="py-prompt">>>> </span>date = cdftime.num2date(t)
<span class="py-prompt">>>> </span><span class="py-keyword">print</span> date
<span class="py-output">2006-03-17 16:04:02</span>
<span class="py-output"></span><span class="py-prompt">>>></span></pre>
<p>The resolution of the transformation operation is 1 second.</p>
<p>Warning: Dates between 1582-10-5 and 1582-10-15 do not exist in the
<code>'standard'</code> or <code>'gregorian'</code> calendars. An
exception will be raised if you pass a 'datetime-like' object in that
range to the <code><a
href="netcdftime.netcdftime.utime-class.html#date2num"
class="link">date2num</a></code> class method.</p>
<p>Words of Wisdom from the British MetOffice concerning reference
dates:</p>
<p>"udunits implements the mixed Gregorian/Julian calendar system,
as followed in England, in which dates prior to 1582-10-15 are assumed to
use the Julian calendar. Other software cannot be relied upon to handle
the change of calendar in the same way, so for robustness it is
recommended that the reference date be later than 1582. If earlier dates
must be used, it should be noted that udunits treats 0 AD as identical to
1 AD."</p>
<!-- ==================== INSTANCE METHODS ==================== -->
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<span class="table-header">Instance Methods</span></td>
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<span class="summary-type"> </span>
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<td><span class="summary-sig"><a href="netcdftime.netcdftime.utime-class.html#__init__" class="summary-sig-name">__init__</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">unit_string</span>,
<span class="summary-sig-arg">calendar</span>=<span class="summary-sig-default"><code class="variable-quote">'</code><code class="variable-string">standard</code><code class="variable-quote">'</code></span>)</span><br />
Returns:
A class instance which may be used for converting times from netCDF
units to datetime objects.</td>
<td align="right" valign="top">
<span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime.__init__">source code</a></span>
</td>
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</td>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr>
<td><span class="summary-sig"><a href="netcdftime.netcdftime.utime-class.html#date2num" class="summary-sig-name">date2num</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">date</span>)</span><br />
Returns <code>time_value</code> in units described by <a
href="netcdftime.netcdftime.utime-class.html#unit_string"
class="link">unit_string</a>, using the specified <a
href="netcdftime.netcdftime.utime-class.html#calendar"
class="link">calendar</a>, given a 'datetime-like' object.</td>
<td align="right" valign="top">
<span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime.date2num">source code</a></span>
</td>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
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<td><span class="summary-sig"><a href="netcdftime.netcdftime.utime-class.html#num2date" class="summary-sig-name">num2date</a>(<span class="summary-sig-arg">self</span>,
<span class="summary-sig-arg">time_value</span>)</span><br />
Return a 'datetime-like' object given a <code>time_value</code> in
units described by <a
href="netcdftime.netcdftime.utime-class.html#unit_string"
class="link">unit_string</a>, using <a
href="netcdftime.netcdftime.utime-class.html#calendar"
class="link">calendar</a>.</td>
<td align="right" valign="top">
<span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime.num2date">source code</a></span>
</td>
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<!-- ==================== INSTANCE VARIABLES ==================== -->
<a name="section-InstanceVariables"></a>
<table class="summary" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="table-header">
<td align="left" colspan="2" class="table-header">
<span class="table-header">Instance Variables</span></td>
</tr>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a name="calendar"></a><span class="summary-name">calendar</span><br />
the calendar used (as specified by the <code>calendar</code>
keyword).
</td>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a name="origin"></a><span class="summary-name">origin</span><br />
datetime instance defining the origin of the netCDF time variable.
</td>
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<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a name="unit_string"></a><span class="summary-name">unit_string</span><br />
a string defining the the netCDF time variable.
</td>
</tr>
<tr>
<td width="15%" align="right" valign="top" class="summary">
<span class="summary-type"> </span>
</td><td class="summary">
<a href="netcdftime.netcdftime.utime-class.html#units" class="summary-name">units</a><br />
the units part of <code>unit_string</code> (i.e.
</td>
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<!-- ==================== METHOD DETAILS ==================== -->
<a name="section-MethodDetails"></a>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr bgcolor="#70b0f0" class="table-header">
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<span class="table-header">Method Details</span></td>
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<a name="__init__"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
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<h3 class="epydoc"><span class="sig"><span class="sig-name">__init__</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">unit_string</span>,
<span class="sig-arg">calendar</span>=<span class="sig-default"><code class="variable-quote">'</code><code class="variable-string">standard</code><code class="variable-quote">'</code></span>)</span>
<br /><em class="fname">(Constructor)</em>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime.__init__">source code</a></span>
</td>
</tr></table>
<dl class="fields">
<dt>Parameters:</dt>
<dd><ul class="nomargin-top">
<li><strong class="pname"><code>unit_string</code></strong> - a string of the form <code>'time-units since
<time-origin>'</code> defining the time units.
<p>Valid time-units are days, hours, minutes and seconds (the
singular forms are also accepted). An example unit_string would
be <code>'hours since 0001-01-01 00:00:00'</code>.</p></li>
<li><strong class="pname"><code>calendar</code></strong> - describes the calendar used in the time calculations. All the
values currently defined in the <a
href="http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.1/cf-conventions.html#time-coordinate"
target="_top">CF metadata convention</a> are accepted. The
default is <code>'standard'</code>, which corresponds to the
mixed Gregorian/Julian calendar used by the <code>udunits
library</code>. Valid calendars are:
<ul>
<li>
<code>'gregorian'</code> or <code>'standard'</code>
(default): Mixed Gregorian/Julian calendar as defined by
udunits.
</li>
<li>
<code>'proleptic_gregorian'</code>: A Gregorian calendar
extended to dates before 1582-10-15. That is, a year is a
leap year if either (i) it is divisible by 4 but not by 100
or (ii) it is divisible by 400.
</li>
<li>
<code>'noleap'</code> or <code>'365_day'</code>: Gregorian
calendar without leap years, i.e., all years are 365 days
long.
</li>
<li>
<code>'all_leap'</code> or <code>'366_day'</code>: Gregorian
calendar with every year being a leap year, i.e., all years
are 366 days long. -<code>'360_day'</code>: All years are 360
days divided into 30 day months. -<code>'julian'</code>:
Proleptic Julian calendar, extended to dates after 1582-10-5.
A year is a leap year if it is divisible by 4.
</li>
</ul></li>
</ul></dd>
<dt>Returns:</dt>
<dd>A class instance which may be used for converting times from
netCDF units to datetime objects.</dd>
</dl>
</td></tr></table>
</div>
<a name="date2num"></a>
<div>
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cellspacing="0" width="100%" bgcolor="white">
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<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">date2num</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">date</span>)</span>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime.date2num">source code</a></span>
</td>
</tr></table>
<p>Returns <code>time_value</code> in units described by <a
href="netcdftime.netcdftime.utime-class.html#unit_string"
class="link">unit_string</a>, using the specified <a
href="netcdftime.netcdftime.utime-class.html#calendar"
class="link">calendar</a>, given a 'datetime-like' object.</p>
<p>The datetime object must represent UTC with no time-zone offset. If
there is a time-zone offset implied by <a
href="netcdftime.netcdftime.utime-class.html#unit_string"
class="link">unit_string</a>, it will be applied to the returned numeric
values.</p>
<p>Resolution is 1 second.</p>
<p>If <code>calendar = 'standard'</code> or <code>'gregorian'</code>
(indicating that the mixed Julian/Gregorian calendar is to be used), an
exception will be raised if the 'datetime-like' object describes a date
between 1582-10-5 and 1582-10-15.</p>
<p>Works for scalars, sequences and numpy arrays. Returns a scalar if
input is a scalar, else returns a numpy array.</p>
<dl class="fields">
</dl>
</td></tr></table>
</div>
<a name="num2date"></a>
<div>
<table class="details" border="1" cellpadding="3"
cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tr valign="top"><td>
<h3 class="epydoc"><span class="sig"><span class="sig-name">num2date</span>(<span class="sig-arg">self</span>,
<span class="sig-arg">time_value</span>)</span>
</h3>
</td><td align="right" valign="top"
><span class="codelink"><a href="netcdftime.netcdftime-pysrc.html#utime.num2date">source code</a></span>
</td>
</tr></table>
<p>Return a 'datetime-like' object given a <code>time_value</code> in
units described by <a
href="netcdftime.netcdftime.utime-class.html#unit_string"
class="link">unit_string</a>, using <a
href="netcdftime.netcdftime.utime-class.html#calendar"
class="link">calendar</a>.</p>
<p>dates are in UTC with no offset, even if <a
href="netcdftime.netcdftime.utime-class.html#unit_string"
class="link">unit_string</a> contains a time zone offset from UTC.</p>
<p>Resolution is 1 second.</p>
<p>Works for scalars, sequences and numpy arrays. Returns a scalar if
input is a scalar, else returns a numpy array.</p>
<p>The datetime instances returned by <code>num2date</code> are 'real'
python datetime objects if the date falls in the Gregorian calendar (i.e.
<code>calendar='proleptic_gregorian'</code>, or <code>calendar =
'standard'/'gregorian'</code> and the date is after 1582-10-15).
Otherwise, they are 'phony' datetime objects which are actually instances
of netcdftime.datetime. This is because the python datetime module
cannot handle the weird dates in some calendars (such as
<code>'360_day'</code> and <code>'all_leap'</code>) which do not exist in
any real world calendar.</p>
<dl class="fields">
</dl>
</td></tr></table>
</div>
<br />
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cellspacing="0" width="100%" bgcolor="white">
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<span class="table-header">Instance Variable Details</span></td>
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<a name="units"></a>
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cellspacing="0" width="100%" bgcolor="white">
<tr><td>
<h3 class="epydoc">units</h3>
the units part of <code>unit_string</code> (i.e. 'days', 'hours',
'seconds').
<dl class="fields">
</dl>
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