Opening files using the with statement is recommended because it ensures that the file is automatically closed at the ends of the with the statement.
# Open file -> close it, or use "with as": # r - read, w - write, a - append, r+ - read and write >>> with open('filename.txt', 'r') as file_object: ... content = file_object.read() ... print(type(content)) ... print(content) ... print(content.rstrip()) <class 'str'> line 1 in the file line 2 in the file line 3 in the file line 1 in the file line 2 in the file line 3 in the file #The blank line in the second print appears #because read() returns an empty string when it reaches the end of the file => rstrip() # line into the list: >>> with open('filename.txt', 'r') as file_object: ... lines = file_object.readlines() >>> print(lines) ['line 1 in the file\n', 'line 2 in the file\n', 'line 3 in the file\n'] >>> for line in lines: ... print(line.rstrip()) line 1 in the file line 2 in the file line 3 in the file #to scan a text file line by line, file iterators are often your best option: >>> for line in open('myfile'): # Use file iterators, not reads ... print(line, end='') ... hello text file goodbye text file
Standard exceptions and users exceptions
It’s better to catch and work with the specific exception
try/except could include:
- else, that will be executed if no exception occurred
- finally, will be executed no matter what (good to closed sockets or files)
Access to Exception
1. Using as: Each error has some attributes that could be used like OSError has errno and strerror, that could be used for debugging etc.
2. Using args: custom message and can do anything you would like
Assert of True – nothing
Assert of False – AssertionsError exception
Just for developers during writing the code. No need to use it for the user input check.