Computer and Programming Foundations: Files, Exception Handling, and Modules

Comprehensive review flashcards covering File I/O, Exception Handling, and Modules/Packages based on Computer Foundations lecture material.

Why is it necessary to store data in files rather than relying solely on variables in RAM?

Data stored in variables in RAM disappears once the program stops running; saving data in a file allows it to reside in permanent storage and be retrieved later.

What is the difference between an input file and an output file?

An input file is a file from which data is read (copied from the file into RAM variables), whereas an output file is a file to which data is written (copied from RAM variables to permanent storage).

What are the three mandatory steps when working with an I/O file in a program?

1. Open the file (creates a connection between the file and program); 2. Process the file (read data from or write data to the file); 3. Close the file (disconnects the file from the program).

What is a file extension, and what role does it serve?

A file extension is a short sequence of characters preceded by a period at the end of a filename (such as .py, .cpp, .dat, .txt) that indicates the type of data stored in the file.

What are the standard path separators for Windows and Mac operating systems?

Windows uses a backslash ($\backslash$), while Mac uses a forward slash ($/$).

What are the effects of the file modes 'r', 'w', 'a', and 'r+' when used in the open() function?

'r' opens for reading only (default mode); 'w' opens for writing only and overwrites any existing content; 'a' opens for writing only with appending; 'r+' is an update mode allowing both reading and writing simultaneously.

How do read(), readlines(), and readline() differ in how they retrieve file content?

read() reads the entire file as a single string; readlines() reads the entire file into a list of strings where each element represents a single line ending in \n; readline() reads one line at a time and returns it as a string.

Why can read() and readlines() only be used once without closing and reopening a file?

Both methods read file content sequentially until the end of the file (EOF) is reached.

What conversion must occur when reading numeric values from a file in Python, and why?

Python file reading methods read all content as strings; to use the data mathematically, they must be converted to numeric types using the int() or float() functions.

What conversion is required when writing numeric values to a file using the write() method?

The write() method only accepts strings, so numeric values (integers or floating-point numbers) must be converted to string format using the str() function.

What error occurs if Python attempts to open a file for reading that does not exist?

FileNotFoundError (Errno 2: No such file or directory).

What error is raised when attempting to read a non-plain-text file (such as an image) with readlines()?

UnicodeDecodeError (e.g., 'utf-8' codec can't decode byte).

What are the functions of os.path.join() and os.path.sep in Python's os module?

os.path.join() concatenates arguments using the correct OS path separator to ensure portability; os.path.sep stores the specific separator string used by the operating system currently in use.

What does os.path.split(aPath) return?

It splits a path into a 2-item tuple (head, tail), where tail is the last token in the path and head is everything else.

How do os.path.exists(aPath) and os.path.isfile(aPath) differ?

os.path.exists(aPath) returns True if the specified path exists; os.path.isfile(aPath) returns True only if the specified path exists and is an actual file (returning False if it is a directory).

What does the os.listdir(path) function return?

It returns a list containing the base filenames and suffixes of all files in the specified input directory.

What is the primary advantage of using a 'with' statement when opening files in Python?

The with statement automatically closes the file once the block of statements finishes executing, guaranteeing the file is closed even without calling close().

What is an exception in Python?

An error that occurs during program execution.

How does the try / except construct handle exceptions?

Code that may potentially produce an error is placed in the try block; if an exception occurs, remaining statements in the try block are skipped and execution shifts to the except block to handle the error gracefully without crashing.

According to the lecture, what specific circumstance causes a TypeError?

An operation or function is applied to an object of inappropriate type.

According to the lecture, what specific circumstance causes a NameError?

A variable name was used that doesn't exit [exist].

According to the lecture, what specific circumstance causes a ValueError?

A type conversion failed.

According to the lecture, what specific circumstance causes a ZeroDivisionError?

Division by zero attempted.

How can multiple exception types be handled by a single exception handler in Python?

By listing the exception types inside a tuple within the except clause (e.g., except (exceptiontype1, exceptiontype2):).

What occurs when a program executes a raise statement?

It causes an immediate exit from the try block and triggers the execution of the appropriate exception handler.

What happens if an exception is raised within a function but not handled inside that function?

The function immediately exits, and the calling function is checked for an exception handler, continuing up the function call hierarchy until a handler is found or the program terminates.

Under what conditions does the finally clause execute in a try / except construct?

The finally clause always executes as the last code before the try block finishes: if no exception occurs, if an exception is handled, if an unhandled exception occurs (before re-raising), or if a break, continue, or return statement exits the try block.

What is the technical difference between a Python script and a Python module?

A script is code saved in a .py file and executed directly by the interpreter; a module is a file containing Python code meant to be imported and used by scripts, other modules, or the interactive interpreter.

What Python construct ensures that specific code is executed only when the file is run as a script and not when imported as a module?

if name == "main":

What is the difference between 'import moduleName' and 'from moduleName import featureName'?

'import moduleName' imports the module and requires accessing its contents via dot notation (moduleName.feature); 'from moduleName import featureName' imports the specific feature so it can be called directly without dot notation.

What is a package in Python, and how is it imported?

A package is a directory of modules that, when imported using the directory name, provides access to all modules stored within it.

What file must be present inside a directory for Python to treat it as a package?

A file named init.py (which is often empty, but may contain package initialization code).

Based on the package hierarchy diagram shown below, what subdirectories are grouped under the top-level 'game' package, and what files do they contain?

The package contains two subdirectories: 'sound' (containing music.py, effects.py, and speech.py) and 'graphics' (containing models.py, textures.py, and terrain.py).

What are the capabilities of the Standard Library modules csv, zipfile, and SimpleHTTPServer?

csv manipulates (reads/writes) CSV files; zipfile creates and reads .zip archive files; SimpleHTTPServer provides a complete, working Web server.

What do the random(), randint(low, high), and choice(stringList) functions in Python's random module do?

random() returns a floating-point number between $0$ and $1$ (specifically between $0$ and $0.9999$); randint(low, high) generates a random integer between low and high (inclusive); choice(stringList) accepts a list of strings and picks a random word from it.