Reading and writing files

Build the idea

Start with the concept and its key vocabulary.

Key idea

Use OCR ERL file operations and their Python equivalents to write and read text safely.

A file stores data beyond the current program run. It must be opened before reading or writing and closed afterwards. ERL uses open, readLine, writeLine, close, endOfFile and newFile. Python opens a file with a mode: 'r' reads and 'w' writes a new or replaced file. Python write does not automatically add a line break, so add \n when a complete line is required.

File

A named collection of data stored outside the program's variables.

Open

Prepare a file for reading or writing and obtain a file handle.

File handle

The program value used to access an open file.

End of file

The position after the final item in a file.

Keep these in mind

ERL: myFile = open(filename), then myFile.readLine() or myFile.writeLine(data).
ERL newFile(filename) creates a new empty file.
myFile.endOfFile() supports a loop that reads until no lines remain.
Python mode r reads; mode w creates or overwrites for writing.
Close the file when finished so buffered changes are saved.
A file procedure should use its data and filename parameters instead of asking for replacement input.

Build the idea

Start with the concept and its key vocabulary.

Key idea

Use OCR ERL file operations and their Python equivalents to write and read text safely.

File

A named collection of data stored outside the program's variables.

Open

Prepare a file for reading or writing and obtain a file handle.

File handle

The program value used to access an open file.

End of file

The position after the final item in a file.

Keep these in mind

ERL: myFile = open(filename), then myFile.readLine() or myFile.writeLine(data).
ERL newFile(filename) creates a new empty file.
myFile.endOfFile() supports a loop that reads until no lines remain.
Python mode r reads; mode w creates or overwrites for writing.
Close the file when finished so buffered changes are saved.
A file procedure should use its data and filename parameters instead of asking for replacement input.