PrePy (Jython API documentation)
Date: 2020-03-21

org.python.core

## Class PrePy

- java.lang.Object
- - org.python.core.PrePy

- Direct Known Subclasses:
    Py

      public class PrePy
      extends java.lang.Object

  This class is part of the Jython run-time system, and contains only "pre-Python" data and methods that may safely be used before the type system is ready. The Jython type system springs into existence in response to a program's first use of any `PyObject`, for example when creating the first interpreter. When preparing an application (from the command line options, say) for creation of the first interpreter, it useful to defer type system creation until pre-Python configuration is complete. See PEP 432 for further rationale.

  Creation of the type system may happen as a side effect of referring using (almost) any object from a class that statically refers to a `PyObject`, for example `Py` or `PySystemState`. The present class is intended to hold utility methods and configuration useful in the pre-Python phase.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `COMMENT` `Options.verbose` level providing detail during correct functioning.
    `static int` | `DEBUG` `Options.verbose` level providing detail in support of debugging or tracing.
    `static int` | `ERROR` `Options.verbose` level indicating an error that prevents correct results.
    `static int` | `MESSAGE` `Options.verbose` level for messages that confirm correct functioning.
    `static int` | `WARNING` `Options.verbose` level indicating an unexpected event, still working correctly.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `PrePy()`

  - ### Method Summary

    All Methods Static Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static java.lang.String` | `getCommandResult(java.lang.String... command)` Run a command as a sub-process and return as the result the first line of output that consists of more than white space.
    `static java.lang.String` | `getDefaultBinDir()` Infers the usual Jython bin-dir from the position of the jar-file returned by `getJarFileName()` byr replacing the file name with "bin".
    `static java.lang.String` | `getDefaultExecutableName()` Infers the usual Jython executable name from the position of the jar-file returned by `getJarFileName()` by replacing the file name with "bin/jython".
    `static java.lang.String` | `getJarFileName()` Utility-method to obtain the name (including absolute path) of the currently used jython-jar-file.
    `static java.lang.String` | `getJarFileNameFromURL(java.net.URL url)` Return the path in the file system (as a string) of a JAR located using the URL of a class file that it contains.
    `static java.util.logging.Level` | `getLoggingLevel()` Convenience function to get the effective level of Logger "org.python".
    `static java.util.Properties` | `getSystemProperties()` Get the System properties if we are allowed to.
    `static java.lang.String` | `getSystemProperty(java.lang.String key, java.lang.String defaultValue)` Get a System property if it is defined, not null, and we are allowed to access it, otherwise return the given default.
    `static boolean` | `haveConsole()` Return `true` iff the console is accessible through System.console().
    `static void` | `increaseLoggingLevel(int n)` Adjust the level of the Jython logger "org.python" using the traditional "verbosity" system: the bigger the number, the lower the logging threshold.
    `static boolean` | `isInteractive()` Determine whether standard input is an interactive stream.
    `static boolean` | `isInteractive(java.io.InputStream fp, java.lang.String filename)` Check whether an input stream is interactive.
    `static java.util.logging.Level` | `levelFromVerbosity(int verbosity)` Translate from the traditional "verbosity" system to JUL Level.
    `static void` | `maybeWrite(java.lang.String type, java.lang.String msg, int verbosity)` Log a message at a specified level (if that level is not below the threshold).
    `static java.util.logging.Level` | `setLoggingLevel(java.util.logging.Level newLevel)` Set the level of the Jython logger "org.python" using the standard `java.util.logging` scale.
    `static int` | `verbosityFromLevel(java.util.logging.Level level)` Translate from JUL Level to equivalent in the traditional "verbosity" system.
    `static void` | `writeComment(java.lang.String type, java.lang.String msg)` Submit a message to logging at the severity level COMMENT.
    `static void` | `writeDebug(java.lang.String type, java.lang.String msg)` Submit a message to logging at the severity level DEBUG.
    `static void` | `writeError(java.lang.String type, java.lang.String msg)` Submit a message to logging at the severity level ERROR.
    `static void` | `writeMessage(java.lang.String type, java.lang.String msg)` Submit a message to logging at the severity level MESSAGE.
    `static void` | `writeWarning(java.lang.String type, java.lang.String msg)` Submit a message to logging at the severity level WARNING.

    - ### Methods inherited from class java.lang.Object

      `equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### ERROR

          public static final int ERROR

      `Options.verbose` level indicating an error that prevents correct results.
      See Also:
        Constant Field Values

    - #### WARNING

          public static final int WARNING

      `Options.verbose` level indicating an unexpected event, still working correctly.
      See Also:
        Constant Field Values

    - #### MESSAGE

          public static final int MESSAGE

      `Options.verbose` level for messages that confirm correct functioning.
      See Also:
        Constant Field Values

    - #### COMMENT

          public static final int COMMENT

      `Options.verbose` level providing detail during correct functioning.
      See Also:
        Constant Field Values

    - #### DEBUG

          public static final int DEBUG

      `Options.verbose` level providing detail in support of debugging or tracing.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### PrePy

          public PrePy()

  - ### Method Detail

    - #### levelFromVerbosity

          public static java.util.logging.Level levelFromVerbosity(int verbosity)

      Translate from the traditional "verbosity" system to JUL Level. We allow Jython verbosity values beyond the conventional range, treating values <`ERROR` as `ERROR` (that is `Level.SEVERE`) and values >`DEBUG` (that is `Level.FINE`) as `FINER`, `FINEST` and `ALL`.
      Parameters:
        `verbosity` - any integer verbosity, where the runtime default `MESSAGE` = 1
      Returns:
        a corresponding level where the default `MESSAGE` produces `Level.INFO`.

    - #### verbosityFromLevel

          public static int verbosityFromLevel(java.util.logging.Level level)

      Translate from JUL Level to equivalent in the traditional "verbosity" system. We return Jython verbosity values beyond the conventional range, enough to enumerate the Java standard levels (e.g `FINER` returns 4 and `ALL` returns 6 ).
      Parameters:
        `level` - `java.util.logging.Level` to translate.
      Returns:
        integer verbosity, where the runtime default `INFO` = 1

    - #### getLoggingLevel

          public static java.util.logging.Level getLoggingLevel()

      Convenience function to get the effective level of Logger "org.python".

    - #### setLoggingLevel

          public static java.util.logging.Level setLoggingLevel(java.util.logging.Level newLevel)

      Set the level of the Jython logger "org.python" using the standard `java.util.logging` scale. For backward compatibility with the traditional "verbosity" system, make a corresponding setting of `Options.verbose`.
      Parameters:
        `newLevel` - to set
      Returns:
        previous logging level

    - #### increaseLoggingLevel

          public static void increaseLoggingLevel(int n)

      Adjust the level of the Jython logger "org.python" using the traditional "verbosity" system: the bigger the number, the lower the logging threshold. This is primarily for the command-line Jython, where each "-v" increases the verbosity by one, on the `java.util.logging` scale.
      Parameters:
        `n` - increment on the scale `1=INFO, 2=CONFIG, 3=FINE, ...`

    - #### maybeWrite

          public static void maybeWrite(java.lang.String type,
                                        java.lang.String msg,
                                        int verbosity)

      Log a message at a specified level (if that level is not below the threshold).

    - #### writeError

          public static void writeError(java.lang.String type,
                                        java.lang.String msg)

      Submit a message to logging at the severity level ERROR.

    - #### writeWarning

          public static void writeWarning(java.lang.String type,
                                          java.lang.String msg)

      Submit a message to logging at the severity level WARNING.

    - #### writeMessage

          public static void writeMessage(java.lang.String type,
                                          java.lang.String msg)

      Submit a message to logging at the severity level MESSAGE.

    - #### writeComment

          public static void writeComment(java.lang.String type,
                                          java.lang.String msg)

      Submit a message to logging at the severity level COMMENT.

    - #### writeDebug

          public static void writeDebug(java.lang.String type,
                                        java.lang.String msg)

      Submit a message to logging at the severity level DEBUG.

    - #### getSystemProperties

          public static java.util.Properties getSystemProperties()

      Get the System properties if we are allowed to. Configuration values set via `-Dprop=value` to the java command will be found here. If a security manager prevents access, we will return a new (empty) object instead.
      Returns:
        `System` properties or a new `Properties` object

    - #### getSystemProperty

          public static java.lang.String getSystemProperty(java.lang.String key,
                                                           java.lang.String defaultValue)

      Get a System property if it is defined, not null, and we are allowed to access it, otherwise return the given default.
      Parameters:
        `key` - of the entry to return
        `defaultValue` - to return if null or disallowed
      Returns:
        property value or given default

    - #### isInteractive

          public static boolean isInteractive()

      Determine whether standard input is an interactive stream. If the Java system property `python.launcher.tty` is defined and equal to `true` or `false`, then that provides the result. This property is normally supplied by the launcher. In the absence of this certainty, we use `haveConsole()`.
      Returns:
        true if (we think) standard input is an interactive stream

    - #### haveConsole

          public static boolean haveConsole()

      Return `true` iff the console is accessible through System.console().

    - #### isInteractive

          public static boolean isInteractive(java.io.InputStream fp,
                                              java.lang.String filename)

      Check whether an input stream is interactive. This emulates CPython `Py_FdIsInteractive` within the constraints of pure Java. The input stream is considered ``interactive'' if either
      1. it is `System.in` and `isInteractive()` is `true`, or
      2. the `-i` flag was given (`Options.interactive`=`true`), and the filename associated with it is `null` or `"<stdin>"` or `"???"`.
      Parameters:
        `fp` - stream (tested only for `System.in`)
        `filename` -
      Returns:
        true iff thought to be interactive

    - #### getDefaultExecutableName

          public static java.lang.String getDefaultExecutableName()

      Infers the usual Jython executable name from the position of the jar-file returned by `getJarFileName()` by replacing the file name with "bin/jython". This is intended as an easy fallback for cases where `sys.executable` is `None` due to direct launching via the java executable.

      Note that this does not necessarily return the actual executable, but instead infers the place where it is usually expected to be. Use `sys.executable` to get the actual executable (may be `None`.

      Returns:
        usual Jython-executable as absolute path

    - #### getDefaultBinDir

          public static java.lang.String getDefaultBinDir()

      Infers the usual Jython bin-dir from the position of the jar-file returned by `getJarFileName()` byr replacing the file name with "bin". This is intended as an easy fallback for cases where `sys.executable` is `null` due to direct launching via the java executable.

      Note that this does not necessarily return the actual bin-directory, but instead infers the place where it is usually expected to be.

      Returns:
        usual Jython bin-dir as absolute path

    - #### getJarFileName

          public static java.lang.String getJarFileName()

      Utility-method to obtain the name (including absolute path) of the currently used jython-jar-file. Usually this is jython.jar, but can also be jython-dev.jar or jython-standalone.jar or something custom.
      Returns:
        the full name of the jar file containing this class, `null` if not available.

    - #### getJarFileNameFromURL

          public static java.lang.String getJarFileNameFromURL(java.net.URL url)

      Return the path in the file system (as a string) of a JAR located using the URL of a class file that it contains. Classes in Java can be asked for the URL of their associated resources (including their own class definition), and so the caller of this method may present such a URL as the basis for locating the JAR from which it came.

      Three protocols are supported, Java JAR-file protocol, and two JBoss protocols "vfs" and "vfszip".

      The JAR-file protocol URL, which must be a `jar:file:` reference to a contained element (that is, it has a "!/" part) is able to identify an actual JAR in a file system that may then be opened using `jarFile = new JarFile(jarFileName)`. The path to the JAR is returned. If the JAR is accessed by another mechanism (`http:` say) this will fail.

      The JBoss URL must be a reference to a class in `vfs:<JAR>/org/python/core/`, or the same thing using the `vfszip:` protocol, where <JAR> stands for the absolute path to the Jython JAR in VFS. There is no "!/" marker: in JBoss VFS a JAR is treated just like a directory and can no longer be opened as a JAR. The method essentially just swaps a VFS protocol for the Java `file:` protocol. The path returned will be correct only if this naive swap is valid.

      Parameters:
        `url` - into the JAR
      Returns:
        the file path or `null` in the event of a detectable error

    - #### getCommandResult

          public static java.lang.String getCommandResult(java.lang.String... command)

      Run a command as a sub-process and return as the result the first line of output that consists of more than white space. It returns "" on any kind of error.
      Parameters:
        `command` - as strings (as for `ProcessBuilder`)
      Returns:
        the first line with content, or ""

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