And you may also have seen another type of file, with a name ending in. These are a bit harder to see on Python 3—instead of ending up in the same directory as your. And maybe you've heard that this is some kind of time-saver that prevents Python from having to re-parse your source code every time it runs.
But beyond "oh, that's Python bytecode," do you really know what's in those files and how Python uses them? If not, today's your lucky day! I'll take you through what Python bytecode is, how Python uses it to execute your code, and how knowing about it can help you.
Python is often described as an interpreted language—one in which your source code is translated into native CPU instructions as the program runs—but this is only partially correct. Python, like many interpreted languages, actually compiles source code to a set of instructions for a virtual machine, and the Python interpreter is an implementation of that virtual machine.
This intermediate format is called "bytecode. So those. If you type up that hello function and use the CPython interpreter to run it, the above listing is what Python will execute. It might look a little weird, though, so let's take a deeper look at what's going on. Cheat sheet: Python 3. That is, it's oriented entirely around stack data structures where you can "push" an item onto the "top" of the structure, or "pop" an item off the "top".
Most of Python's bytecode instructions manipulate the evaluation stack of the current call-stack frame, although there are some instructions that do other things like jump to specific instructions or manipulate the block stack.
The corresponding compiler of C language on different platforms will compile it into different machine code files, and different machine code files can only run in this platform. The execution process of java file is as follows: java compiles the source file into a.
As mentioned earlier, "the. It is not hard to think that as long as another language also follows the JVM specification and can compile its source file into a. Let's take a look at the official picture:. There are 17 kinds of constants, which are listed in the following table with corresponding marks. Each label byte must be followed by two or more bytes to provide information about a specific constant.
The format of the additional information depends on the tag byte, that is, the contents of the info array vary with the value of the tag. When set, the interpretation of each flag is specified in the following table. Object This is the only class or interface that does not have a direct superclass. The field table contains only fields declared by this class or interface, not fields inherited from a superclass or interface.
The field structure is as follows:. The method table does not contain a representation of methods inherited from a superclass or a superinterface. Here however, more information is encoded. To compute the number of elements to pop from the stack, we then need to get:. Here, that gives us 6, the number of elements to pop before accessing the function name.
Even if the bytecode is a fairly small language, building a reliable CFG requires more details than this blog post can allow, so for an actual implementation of a CFG construction, you can have a look at equip.
Building the CFG for a function means creating basic blocks sequence of opcodes that have unconditional execution — except when an exception can occur , and connecting them in a graph that contains conditions on branches. In our case, we only have True , False , and Unconditional branches.
In this bytecode, we have 5 instructions that change the structure of the CFG so adds constraints or allows for quick exit :. Check out this question for java byte code editors. What is the underlying problem you need to solve? Abhishek What information are you seeking in the class file?
I found a website which allows you to input java code and get the bytecode as the output. I had this need for creating a forked java process which could delegate to the class loader in this process without having to override it.
If you implement your own classloader, you get to load the bytecode into a class. But, if you start with a class you can't convert it to bytecode for shipping to an external process. Add a comment. Active Oldest Votes. For example: javap -c com. Jesper Jesper k 44 44 gold badges silver badges bronze badges. By default private methods are not included. Use -p to include them as well.
For me only worked with the file name extension seems to be optional though , but not with the fully qualified class name: javap -c -p MyClass. MyClass will print the code on the terminal stdout. I prefer javap -c -p com. Andreas Dolk Andreas Dolk k 16 16 gold badges silver badges bronze badges. To view the bytecodes Forget javap!
0コメント