How to convert "str" to "int"

[colt]

Hello I am currently reading a file in binary mode.

I do the reading with

1 2	with open (args.rom_path, 'rb') as file:         rom_bytes = file.read ()

Then part of these rom_bytes are transferred to another variable with:

1	self.header = rom_bytes [0:HEADER_SIZE]

and finally, one of the bytes stored in the header are transferred to a variable:

1	self.temp = self.header [4]

This value it is "2" in unsigned 8 bit, as a hexadecimal editor informs me.

However, the above line of code causes:

TypeError: 'int' does not support the buffer interface

So I need to convert into an int, a value that it is what, a byte?

How can I do it?

[scidam]

Take a look at the struct module.

1 2 3

import struct four_bytes = b'abcd'  # sample bytesting struct.unpack("I", four_bytes) # interpret bytesting as unsigned int

[Gribouillis]

However, the above line of code causes:

Are you sure it's this line that causes this error message? If 'header' is a bytes string (which you can check by printing the type of the variable) there should be no problem accessing header[4], and it must be an integer. In the worst case it could raise an IndexError.

[colt]

Take a look at the struct module.

1 2 3

import struct four_bytes = b'abcd'  # sample bytesting struct.unpack("I", four_bytes) # interpret bytesting as unsigned int

From what I see the difference is that you used "I" instead my "h". I changed it and didn't change the error message.

Are you sure it's this line that causes this error message? If 'header' is a bytes string (which you can check by printing the type of the variable) there should be no problem accessing header[4], and it must be an integer. In the worst case it could raise an IndexError.

It says line 11, which is the one that uses struct.unpack. I checked the type and it shows

<class 'bytes'>

[Gribouillis]

It says line 11, which is the one that uses struct.unpack

There is no struct.unpack in the original post. It will be much easier if you post the whole code that throws the exception, so that we can run it by ourselves.

[colt]

It says line 11, which is the one that uses struct.unpack

There is no struct.unpack in the original post. It will be much easier if you post the whole code that throws the exception, so that we can run it by ourselves.

Ok here it is:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

from abc import ABCMeta, abstractmethod import argparse   HEADER_SIZE = 16 KB_SIZE = 16384   class Instruction (object):     __metaclass_ = ABCMeta               def __init__ (self,identification_byte):         identity_byte = identification_byte       def test (self):         print ("BOTO")       @abstractmethod     def process (self):         print ("Identifier Byte: {}".format(self.identity_byte))       @abstractmethod     def process2 (self):         print ("Identifier Byte2: ", self.identity_byte)             class LDAInstruction (Instruction):     def process (self):         super.process ()       def process2 (self):         super.process()   class ROM (object) :     def __init__ (self, rom_bytes):         self.header = rom_bytes [0:HEADER_SIZE]         self.temp = self.header [4]         print (type (self.header))         self.num_prg_blocks = struct.unpack ("I", self.temp)         print (type (self.num_prg_blocks))         self.data_bytes = rom_bytes [HEADER_SIZE:HEADER_SIZE + (16 + KB_SIZE * int (self.num_prg_blocks))]         self.total_size = 16 + KB_SIZE * self.num_prg_blocks       def get_byte (self, pc):         return  (self.data_bytes [pc])   class CPU (object):     def __init__(self, rom_bytes):         self.registers = []         self.rom = ROM (rom_bytes)         self.pc = 0       def process_instructions (self):         for byte in self.rom.data_bytes:             byte = self.rom.get_byte (self.pc)             self.pc+=1             print (byte)             if (byte == 169):                 instruction = Instruction (byte)                 instruction.process ()                 instruction.process2 ()             if (self.pc == 3):                 break   def main ():       parser = argparse.ArgumentParser (description='NES EMULATOR');     parser.add_argument ('rom_path',metavar='R',type=str,help='path to the rom')     args=parser.parse_args()       with open (args.rom_path, 'rb') as file:         rom_bytes = file.read ()                  cpu = CPU(rom_bytes)     cpu.process_instructions ()   if __name__ == '__main__':     main ()

However, this will not run because it needs a file as a command line argument.

[Gribouillis]

Could it be an error similar to this one ?

1 2 3 4 5 6 7 8

>>> rom_bytes = b'hello world' >>> import struct >>> struct.unpack("I", rom_bytes[4]) Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: a bytes-like object is required, not 'int' >>> struct.unpack("I", rom_bytes[:4]) (1819043176,)

[colt]

Could it be an error similar to this one ?

1 2 3 4 5 6 7 8

>>> rom_bytes = b'hello world' >>> import struct >>> struct.unpack("I", rom_bytes[4]) Traceback (most recent call last):   File "<stdin>", line 1, in <module> TypeError: a bytes-like object is required, not 'int' >>> struct.unpack("I", rom_bytes[:4]) (1819043176,)

I don't understand why would be, since is a different error message.

Anyway, I don't know why, but now the code is working on python 3.2, since it converts the values to int. However in 2.6 where the type is 'str', first I receive

self.data_bytes = rom_bytes [HEADER_SIZE:HEADER_SIZE + (16 + KB_SIZE *(self.num_prg_blocks))]
TypeError: unsupported operand type(s) for +: 'int' and 'str'

Then adding a int before with:

1	self.data_bytes = rom_bytes [HEADER_SIZE:HEADER_SIZE + (16 + KB_SIZE * int (self.num_prg_blocks))]

I receive:

ValueError: invalid literal for int() with base 10: '\x02'

finally doing this:

1 2 3

self.temp = self.num_prg_blocks         struct.unpack ("I", self.temp)         self.data_bytes = rom_bytes [HEADER_SIZE:HEADER_SIZE + (16 + KB_SIZE * self.temp)]

makes me receive on python 2.6

struct.error: unpack requires a string argument of length 4

and on python 3.2

TypeError: 'int' does not support the buffer interface

What shall be my next step?

[Gribouillis]

I don't know why, but now the code is working on python 3.2, since it converts the values to int.

That's because in python 3 a bytes string is a sequence of small integers:

1 2 3 4

>>> # python 3 >>> x = b'\x02' >>> x[0] 2

in python 2

1 2 3 4

>>> # python 2 >>> x = '\x02' >>> x[0] '\x02'

In python 2 you can convert a one character string to int by using the ord function

1 2	>>> ord(x[0]) 2

But when calling struct.unpack ("I", self.temp), make sure self.temp is a 4 bytes string.

Finally, do you have to use python 2? Don't use it, it's dead.

[colt]

I don't know why, but now the code is working on python 3.2, since it converts the values to int.

That's because in python 3 a bytes string is a sequence of small integers:

1 2 3 4

>>> # python 3 >>> x = b'\x02' >>> x[0] 2

in python 2

1 2 3 4

>>> # python 2 >>> x = '\x02' >>> x[0] '\x02'

In python 2 you can convert a one character string to int by using the ord function

1 2	>>> ord(x[0]) 2

But when calling struct.unpack ("I", self.temp), make sure self.temp is a 4 bytes string.

Finally, do you have to use python 2? Don't use it, it's dead.

Tried

1	self.num_prg_blocks = ord (self.header [4])

and it solved this issue with old python, but with the new python I receive:

TypeError: ord() expected string of length 1, but int found

To answer, I do not HAVE to use it, as mandatory