Python provides inbuilt functions for creating, writing and reading files. There are two types of files that can be handled in python, normal text files and binary files (written in binary language,
1s). In this article, we are going to study about reading line by line from a file.
Reading line by line
readlines() is used to read all the lines at a single go and then return them as each line a string element in a list. This function can be used for small files, as it reads the whole file content to the memory, then split it into separate lines. We can iterate over the list and strip the newline
'\n' character using
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readline() function reads a line of the file and return it in the form of the string. It takes a parameter n, which specifies the maximum number of bytes that will be read. However, does not reads more than one line, even if n exceeds the length of the line. It will be efficient when reading a large file because instead of fetching all the data in one go, it fetches line by line.
readline() returns the next line of the file which contains a newline character in the end. Also, if end of the file is reached, it will return an empty string.
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Using for loop
An iterable object is returned by
open() function while opening a file. This final way of reading in a file line-by-line includes iterating over a file object in a
for loop. Doing this we are taking advantage of a built-in Python functionality that allows us to iterate over the file object implicitly using a
for loop in combination of using the iterable object. This approach takes fewer lines of code, which is always the best practice worthy of following.
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In the above approaches, every time the file is opened it is needed to be closed explicitly. If one forgets to close the file, it may introduce several bugs in the code, i.e. many changes in files do not go into effect until the file is properly closed. To prevent this
with statement can be used.
with statement in Python is used in exception handling to make the code cleaner and much more readable. It simplifies the management of common resources like file streams. Observe the following code example on how the use of with statement makes code cleaner. There is no need to call
file.close() when using with statement. The
with statement itself ensures proper acquisition and release of resources.
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