Reading bytes and converting to int

[joao]

On Saturday, 25 August 2012 at 20:03:38 UTC, Jonathan M Davis 
wrote:
> On Saturday, August 25, 2012 21:50:58 joao wrote:
>> Thanks everyone, I solved the problem.
>> I didn't understand these bitmanip methods so I searched and
>> found a function to do what I wanted:
>> 
>> string b = "\x24\x10\x00\x00";
>> uint i = byteToInt(b);
>> uint byteToInt(string b) {
>> 	 return b[0] | b[1] << 8 | b[2] << 16 | b[3] << 24;
>> }
>> 
>> => 4132
>
> What's hard to understand about them? I thought that they were 
> very
> straightforward.
>
> This will do essentially the same thing:
>
> import std.bitmanip;
> import std.system;
>
> void main()
> {
>     ubyte[] b = [0x24, 0x10, 0x00, 0x00];
>     auto i = peek!(uint, Endian.littleEndian)(b);
>     assert(i == 4132);
> }
>
> Use peek if you don't want to consume the buffer and read if 
> you do.
>
> - Jonathan M Davis

It's not hard, sorry, it's because I'm a begginner.
So, all I wanted to do was to open a file and read the first 4 
bytes and then return the int value. The last part I managed to 
do.
But the first I'm trying.

In Python it is something like this:
f = open('filename')
s = f.read(4)
...
In D I don't know yet. I'm trying to do:
File f = File('filename')
Then I want to read just 4 bytes. I still don't know what method 
is :P