org.python.core.PyShadowString Maven / Gradle / Ivy
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package org.python.core;
import java.util.regex.Pattern;
import org.python.expose.ExposedMethod;
import org.python.expose.ExposedNew;
import org.python.expose.ExposedType;
import org.python.expose.MethodType;
/**
* This class provides a string that sometimes seems to change value, as far as equality tests and
* startswith are concerned. This solves a problem that Jython users sometimes
* experience with libraries that are sensitive to platform.
*
* A library may test for a particular platform in order to adjust to local file name conventions or
* to decide which operating system commands are available. In Jython, os.name and
* sys.platform indicate that Java is the platform, which is necessary information in
* some parts of the standard library, but other libraries assuming CPython then draw incorrect
* conclusions.
*
* With hindsight, a better choice could be made, where sys.platform etc. indicated
* Windows or Posix, and something else indicates the implementation. A change in Jython 2 would
* cause more problems than it solved, but we expect Jython 3 to work that way. In the Python
* Standard Library, the Jython project can make all necessary changes. It can't do anything about
* third-party libraries. But it would be a big help if users could cause sys.platform
* or os.name to appear to have the OS-dependent value as far as those troublesome
* libraries were concerned.
*
* This is what this class achieves. os.name and sys.platform regular
* strings for most purposes, but each has a "shadow" value that is used in contexts the user may
* specify.
*/
@Untraversable
@ExposedType(name = "shadowstr", base = PyString.class, isBaseType = true)
public class PyShadowString extends PyString {
public static final PyType TYPE = PyType.fromClass(PyShadowString.class);
/**
* Contexts (expressed as a {@link PyTuple} of class name and method name) where {@link #shadow}
* is allowed to match as well as the primary value.
*/
protected PyList targets;
/**
* The shadow string is additionally used for some comparisons, especially for __eq__. __eq__
* will evaluate positive if the other string equals the primary value *or* the shadow. The
* shadow persists slicing (is sliced accordingly) and is taken into account by startswith.
*/
protected PyString shadow;
/** Empty string (not very useful but needed for technical reasons). */
public PyShadowString() {
this(Py.EmptyString, Py.EmptyString);
}
/** Construct an instance specifying primary and shadow values. */
public PyShadowString(String primary, String shadow) {
this(TYPE, Py.newString(primary), Py.newString(shadow), new PyList());
}
/** Construct an instance specifying primary and shadow values (bytes objects expected). */
private PyShadowString(PyObject primary, PyObject shadow) {
this(TYPE, primary, shadow, new PyList());
}
private PyShadowString(PyObject primary, PyObject shadow, PyList targets) {
this(TYPE, primary, shadow, targets);
}
public PyShadowString(PyType subtype, PyObject primary, PyObject shadow) {
this(subtype, primary, shadow, new PyList());
}
private PyShadowString(PyType subtype, PyObject primary, PyObject shadow, PyList targets) {
super(subtype, primary.__str__().getString());
this.shadow = shadow.__str__();
this.targets = targets;
}
@ExposedNew
static PyObject shadowstr_new(PyNewWrapper new_, boolean init, PyType subtype, PyObject[] args,
String[] keywords) {
ArgParser ap =
new ArgParser("shadowstr", args, keywords, new String[] {"primary", "shadow"}, 0);
PyObject valueObj = ap.getPyObject(0, Py.EmptyString);
PyObject shadowObj = ap.getPyObject(1, Py.EmptyString);
if (valueObj instanceof PyString && shadowObj instanceof PyString) {
return new PyShadowString(valueObj, shadowObj);
} else {
String message = String.format("arguments must be strings not (%.200s, %.200s)",
valueObj.getType(), shadowObj.getType());
throw Py.TypeError(message);
}
}
/** Convert a PyObject (specifying a regex) to a compiled pattern or null. */
private static Pattern getPattern(PyObject o) {
if (o instanceof PyString) {
return Pattern.compile(o.toString());
} else {
return null;
}
}
/**
* Test whether the current code is executing in of one of the target contexts, by searching up
* the stack for a class and method pait that match.
*
* @return true iff in one of the named contexts
*/
private boolean isTarget() {
// Get a stack trace by constructing an exception here
Exception exc = new Exception();
for (PyObject obj : targets.getList()) {
// Only process proper tuple entries
if (obj instanceof PyTuple && ((PyTuple) obj).__len__() >= 2) {
// Compile the target specification
PyTuple target = (PyTuple) obj;
Pattern clazz = getPattern(target.__finditem__(0));
Pattern method = getPattern(target.__finditem__(1));
// Now scan the stack using this pair of patterns
for (StackTraceElement ste : exc.getStackTrace()) {
if (clazz == null || clazz.matcher(ste.getClassName()).matches()) {
// Either we don't care about the class it matches, and ...
if ((method == null || method.matcher(ste.getMethodName()).matches())) {
// Either we don't care about the method name or it matches
return true;
}
}
}
}
}
// Nothing matched
return false;
}
/** Get the shadow value. */
public PyString getshadow() {
return shadowstr_getshadow();
}
@ExposedMethod
public final PyString shadowstr_getshadow() {
return shadow;
}
/**
* Specify a context (class, method) in which the shadow string is allowed to match.
*
* @param className class name to match or null to match anything.
* @param methodName method name to match or null to match anything.
*/
public void addTarget(String className, String methodName) {
shadowstr_addtarget( //
className == null ? Py.None : Py.newUnicode(className),
methodName == null ? Py.None : Py.newUnicode(methodName));
}
@ExposedMethod(defaults = {"null"})
public final void shadowstr_addtarget(PyObject classname, PyObject methodname) {
// In principle these could be unicode strings
PyTuple entry = new PyTuple(asUnicode(classname), asUnicode(methodname));
targets.add(entry);
}
/** Prepare argument for addtarget, allowing string-like values or None. */
private static PyObject asUnicode(PyObject o) {
if (o == null || o == Py.None) {
return Py.None;
} else if (o instanceof PyString) {
return o.__unicode__();
}
throw Py.TypeError(String.format("string or None required, not %.200s", o.getType()));
}
/**
* Return a list of the tuples specifying the contexts in which the shadow value will be
* consulted during matching.
*/
public PyList getTargets() {
return (PyList) shadowstr_gettargets();
}
@ExposedMethod
public final PyObject shadowstr_gettargets() {
return targets;
}
/**
* Compare this PyShadowString with another PyObject for equality. A
* PyShadowString is equal to the other object if its primary value is equal to it,
* or if its shadow value is equal to the other object and the test is made in one of its target
* contexts. (Two PyShadowString are equal if the primary values are equal, the
* primary of one matches the shadow of the other in the shadow's context, or their shadows
* match and both are in context.
*
* @param other to compare
* @return PyBoolean result (or null if not implemented)
*/
@Override
public PyObject __eq__(PyObject other) {
return shadowstr___eq__(other);
}
@ExposedMethod(type = MethodType.BINARY)
final PyObject shadowstr___eq__(PyObject other) {
// Re-wrap the primary value as a PyString to invoke the right kind of equality test.
PyObject result = testEqual(new PyString(getString()), other);
if (result != Py.False) {
// True, or null if str does not know how to compare with other (so we don't either).
return result;
} else if (targets.isEmpty()) {
// We aren't going to be using our shadow string
return Py.False;
} else {
// Since we have targets, compare the shadow string with the other object.
result = testEqual(shadow, other);
if (result == Py.True) {
// It matches, so the result is true iff we are in a target context
return Py.newBoolean(isTarget());
} else {
return result;
}
}
}
/**
* Test for equality, used as a helper to shadowstr___eq__, dealing with the
* possibility that other is another PyShadowString.
*/
private static final PyObject testEqual(PyString string, PyObject other) {
if (other instanceof PyShadowString) {
return ((PyShadowString) other).shadowstr___eq__(string);
} else {
return string.__eq__(other);
}
}
@Override
public PyObject __getslice__(PyObject start, PyObject stop, PyObject step) {
PyObject primary = super.__getslice__(start, stop, step);
PyObject shadow = this.shadow.__getslice__(start, stop, step);
return new PyShadowString(primary, shadow, targets);
}
@Override
public boolean startswith(PyObject prefix) {
return shadowstr_startswith(prefix, null, null);
}
@Override
public boolean startswith(PyObject prefix, PyObject start) {
return shadowstr_startswith(prefix, start, null);
}
@Override
public boolean startswith(PyObject prefix, PyObject start, PyObject end) {
return shadowstr_startswith(prefix, start, end);
}
@ExposedMethod(defaults = {"null", "null"})
final boolean shadowstr_startswith(PyObject prefix, PyObject startObj, PyObject endObj) {
return super.startswith(prefix, startObj, endObj) //
|| (!targets.isEmpty() && shadow.startswith(prefix, startObj, endObj)
&& isTarget());
}
@Override
public PyString __repr__() {
return shadowstr___repr__();
}
@ExposedMethod
final PyString shadowstr___repr__() {
// What you'd type to get this instance (without targets).
String fmt = "PyShadowString(%.200s, %.200s)";
return Py.newString(String.format(fmt, super.__repr__(), shadow.__repr__()));
}
}