On 29/11/11 21:40, Mayo Adams wrote:
tuple that is in the file, it would be helpful to know what it is. Presumably, a string representing a tuple.
Exactly so, everything in the file is a string. If it's a binary file it is a string of bytes, if it is a text file a string of characters. The interpretation of those bytes or characters is down to the reading program. The program must convert the string into data. The string represents the data that will be eventually created in the computer's memory within the interpreter's execution environment.
representation, I cant immediately see how anything in a script is anything other than a representation of some kind, hence the distinction between representamen and object does no work for me.
While it is in the file it is just a string. a string representation of a program. The interpreter reads that string and converts it into symbol tables, executable objects and data structures. Your program, when it reads a file must do exactly the same, it must convert the string read from the file into whatever data structure it represents and, if necessary, assign that data to a variable for future reference.
The process of reading a string and interpreting its meaning as data is what's known as parsing. There are several parsers available in Python to help with that task, as well as some tools to help you write your own parser. Examples are the csv module, HTMLParser, xpat and ElementTree. But even with these you will often have to do the final type conversion from string to integer or Boolean etc yourself.
The other option is to use binary files where the data is stored in strings of bytes. In this case you still need to interpret the string but you do so by reading the exact number of bytes needed to store the particular data type, for example 4 bytes for a 32 bit integer. You then have to convert those 4 bytes into an integer. Again Python offers some help in the form of the struct module. Binary files are usually more compact than text files storing the same information, but they are far harder to interpret. There are other standard types of binary file and Python offers support for some, most notably there are libraries to read Excel files, various databases and PDF documents. Most of these libraries will also contain functions that help you write data back out to the files in the same format as well.
The goal of all of these libraries is to make it comparatively easy to read a string representation from a file and convert it into real data that we can manipulate in our programs.
HTH, -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
