Interface Interpreter
- All Superinterfaces:
AutoCloseable
- All Known Implementing Classes:
Jep
,SharedInterpreter
,SubInterpreter
Embeds CPython in Java. Each Interpreter instance provides access to a Python
interpreter and maintains an independent global namespace for Python
variables. Values can be passed from Java to Python using the
set(String, Object)
method. Various methods, such as
exec(String)
and invoke(String, Object...)
can be used to
execute Python code. Python variables can be accessed using
getValue(String)
and getValue(String, Class)
.
Methods called on an Interpreter must be called from the same thread that created the instance. To maintain stability, avoid having two Interpreter instances running on the same thread at the same time. Instead provide different threads or close() one before instantiating another on the same thread. Interpreter instances should always be closed when no longer needed to prevent memory leaks.
- Since:
- 3.9
-
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
boolean
Evaluate Python statements.void
Execute an arbitrary number of Python statements in this interpreter.Retrieves a value from this Python interpreter.<T> T
LikegetValue(String)
but allows specifying the return type.Invokes a Python function.Invokes a Python function.Invokes a Python function.void
Runs a Python script.void
Sets the Java Object into the interpreter's global scope with the specified variable name.
-
Method Details
-
invoke
Invokes a Python function.- Parameters:
name
- a Python function name in globals dict or the name of a global object and method using dot notationargs
- args to pass to the function in order- Returns:
- an
Object
value - Throws:
JepException
- if an error occurs
-
invoke
Invokes a Python function.- Parameters:
name
- a Python function name in globals dict or the name of a global object and method using dot notationkwargs
- a Map of keyword args- Returns:
- an
Object
value - Throws:
JepException
- if an error occurs
-
invoke
Invokes a Python function.- Parameters:
name
- a Python function name in globals dict or the name of a global object and method using dot notationargs
- args to pass to the function in orderkwargs
- a Map of keyword args- Returns:
- an
Object
value - Throws:
JepException
- if an error occurs
-
eval
Evaluate Python statements.
In interactive mode, Jep may not immediately execute the given lines of code. In that case, eval() returns false and the statement is stored and is appended to the next incoming string.
If you're running an unknown number of statements, finish with
eval(null)
to flush the statement buffer.Interactive mode is slower than a straight eval call since it has to compile the code strings to detect the end of the block. Non-interactive mode is faster, but code blocks must be complete. For example:
interactive mode == false
jep.eval("if(Test):\n print('Hello world')");
interactive mode == true
jep.eval("if(Test):"); jep.eval(" print('Hello world')"); jep.eval(null);
Also, Python does not readily return object values from eval(). Use
getValue(String)
instead.Note: Interactive mode will be removed in a future release. This method may still be used for executing individual statements. See console.py for an example of how to interactively execute Python using the builtin compile() and exec() functions.
- Parameters:
str
- aString
statement to eval- Returns:
- true if statement complete and was executed.
- Throws:
JepException
- if an error occurs
-
exec
Execute an arbitrary number of Python statements in this interpreter. Similar to the Python builtin exec function.- Parameters:
str
- Python code to exececute- Throws:
JepException
- if an error occurs
-
runScript
Runs a Python script.- Parameters:
script
- aString
absolute path to script file.- Throws:
JepException
- if an error occurs
-
getValue
Retrieves a value from this Python interpreter. Supports retrieving:
- Java objects
- Python None (null)
- Python strings
- Python True and False
- Python numbers
- Python lists
- Python tuples
- Python dictionaries
For Python containers, such as lists and dictionaries, getValue will recursively move through the container and convert each item. If the type of the value retrieved is not supported, Jep will fall back to returning a String representation of the object. This fallback behavior will probably change in the future and should not be relied upon.
- Parameters:
str
- the name of the Python variable to get from the interpreter's global scope- Returns:
- an
Object
value - Throws:
JepException
- if an error occurs
-
getValue
LikegetValue(String)
but allows specifying the return type. If Jep cannot convert the variable to the specified type then a JepException is thrown. This can be used to safely ensure that the return value is an expected type. The following table describes what conversions are currently possible.The valid classes for Python to Java conversions Python Class Java Classes Notes str/unicode String
,Character
Character conversion will fail if the str is longer than 1. bool Boolean
int/long Long
,Integer
,Short
,Byte
Conversion fails if the number is outside the valid range for the Java type float Double
,Float
list, tuple List
, arrayWhen a tuple is converted to a List it is unmodifiable. dict Map
function, method Any FunctionalInterface Buffer Protocol array This includes Python classes such as bytes, bytearray and array.array numpy.ndarray NDArray
Only if Jep was built with numpy support numpy.float64 Double
,Float
numpy.float32 Float
,Double
numpy.int64 Long
,Integer
,Short
,Byte
Conversion fails if the number is outside the valid range for the Java type numpy.int32 Integer
,Long
,Short
,Byte
Conversion fails if the number is outside the valid range for the Java type numpy.int16 Short
,Integer
,Long
,Byte
Conversion fails if the number is outside the valid range for the Java type numpy.int8 Byte
.Short
,Integer
,Long
NoneType Any(null) Jep objects such as PyJObjects and jarrays will be returned if the Java type of the wrapped object is compatible. Anything else String
,PyObject
String conversion will likely be removed in future versions of Jep so it is unsafe to depend on this behavior. - Type Parameters:
T
- the generic type of the return type- Parameters:
str
- the name of the Python variable to get from the interpreter's global scopeclazz
- the Java class of the return type.- Returns:
- a Java version of the variable
- Throws:
JepException
- if an error occurs
-
set
Sets the Java Object into the interpreter's global scope with the specified variable name.- Parameters:
name
- the Python name for the variablev
- anObject
value- Throws:
JepException
- if an error occurs
-
close
- Specified by:
close
in interfaceAutoCloseable
- Throws:
JepException
-