What are some efficient ways to read multiple lines from a file quickly in Python?

Question

What are some efficient ways to read multiple lines from a file quickly in Python?

Currently, I am using the following Python code:

file = open(filePath, "r")
lines=file.readlines()
file.close()

If my file contains multiple lines (10,000 or more), my program tends to slow down when processing more than one file. Is there a way to optimize this process in Python? From what I have read, it seems that readlines stores all lines of the file in memory, causing the slowdown.

I also tried the following code and managed to improve the runtime by 17%:

lines=[line for line in open(filePath,"r")]

Are there any other Python 2.4 modules that could help me speed up this process?

Thanks, Sandhya

python file readlines

Answer 1

Answer №1

for row in data_file:

This creates an iterator that reads the data file one row at a time and then removes the previous row from memory.

A data file itself serves as its own iterator. For example, using iter(data) will return data (unless data is closed). When utilizing a data file as an iterator, typically in a for loop (such as for row in data: process row), the next() method is invoked repeatedly. This function provides the subsequent input row or raises StopIteration upon reaching EOF. To optimize looping over the rows of a data file with a for loop (a frequently performed task), the next() method incorporates a concealed read-ahead buffer. Due to the inclusion of a read-ahead buffer, combining next() with other data file methods (like readline()) does not produce the desired outcome. Nevertheless, resetting the file to an absolute position using seek() will clear the read-ahead buffer. Introduced in version 2.3.

In summary: avoid storing rows in a variable, execute necessary operations directly within the loop.

Answer 2

for row in data_file:

This creates an iterator that reads the data file one row at a time and then removes the previous row from memory.

A data file itself serves as its own iterator. For example, using iter(data) will return data (unless data is closed). When utilizing a data file as an iterator, typically in a for loop (such as for row in data: process row), the next() method is invoked repeatedly. This function provides the subsequent input row or raises StopIteration upon reaching EOF. To optimize looping over the rows of a data file with a for loop (a frequently performed task), the next() method incorporates a concealed read-ahead buffer. Due to the inclusion of a read-ahead buffer, combining next() with other data file methods (like readline()) does not produce the desired outcome. Nevertheless, resetting the file to an absolute position using seek() will clear the read-ahead buffer. Introduced in version 2.3.

In summary: avoid storing rows in a variable, execute necessary operations directly within the loop.

What are some efficient ways to read multiple lines from a file quickly in Python?

Answer №1

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