Python file reading/writing and try/except exception handling patterns explained with a short example each.
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- How do you open a file named 'data.txt' in read mode?
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open('data.txt', 'r')- What does 'r' mode do when opening a file?
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Opens the file for reading. The file must exist or FileNotFoundError is raised.- What does 'w' mode do when opening a file?
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Opens the file for writing. Creates the file if it does not exist, or truncates it if it does.- What does 'a' mode do when opening a file?
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Opens the file for appending. New data is written at the end without truncating existing content.- Why use 'with open(filename) as f:' instead of open() alone?
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The 'with' statement (context manager) automatically closes the file when the block exits, even if an error occurs.- What does the read() method return?
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Returns the entire file contents as a single string.- What does readline() return?
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Returns one line from the file as a string, including the newline character at the end.- What does readlines() return?
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Returns a list of strings, one string per line in the file, each including the newline character.- How do you iterate over lines in a file one at a time?
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Use 'for line in file_object:' to loop through each line without loading the entire file into memory.- What does the write() method do?
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Writes a string to the file. Returns the number of characters written.- What does writelines() do?
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Writes a sequence (list) of strings to the file. Does not add newlines between items.- What is the purpose of a try/except block?
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try contains code that might raise an exception; except handles the error if it occurs.- Why catch specific exceptions instead of using bare 'except:'?
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Specific exceptions allow you to handle different errors differently and avoid catching unexpected errors.- What exception is raised when open() cannot find a file?
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FileNotFoundError (a subclass of OSError).- Can you have multiple except blocks for one try block?
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Yes, each except clause can catch different exception types and handle them separately.
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