python readline vs readlines

python readline vs readlines

Python's built-in readline() and readlines() functions are used to interact with file streams. While they may seem similar, they serve different purposes.

readline() is a function that reads a single line from the specified stream or file object. It returns the entire line including the trailing newline character (n). If the end-of-file marker has been reached, it returns an empty string.

Here's how you can use readline():

with open('file.txt', 'r') as f:
for line in iter(f.readline, 'nn'):  # Read lines until an empty line is encountered
print(line.strip())

In this example, the program opens a file named 'file.txt' and reads its contents line by line. Each line is printed after stripping any leading or trailing whitespace.

On the other hand, readlines() is a function that reads all the lines from the specified stream or file object until an end-of-file marker is reached. It returns all the lines as a list of strings. If the end-of-file marker has been reached before reading the entire file, it returns a truncated list.

Here's how you can use readlines():

with open('file.txt', 'r') as f:
for line in f.readlines():
print(line.strip())

In this example, the program also opens a file named 'file.txt' and reads its contents. However, it stores all the lines in a list and then prints each line after stripping any leading or trailing whitespace.

The key difference between readline() and readlines() is that readline() returns one line at a time, while readlines() returns a list of all the lines. This can be important if you need to process the entire file at once or if the file contains an enormous number of lines.

In addition, readline() can be used with iterators to efficiently read very large files by reading one line at a time:

with open('file.txt', 'r') as f:
for _ in range(1000):  # Read the first 1000 lines
line = f.readline()
if not line:  # Check if we reached the end of file
break
print(line.strip())

In this example, the program reads the first 1000 lines from a file and then breaks. This can be an efficient way to read very large files by processing them one block at a time.

In conclusion, readline() is used when you need to process one line of a file at a time or iterate over the lines in a file, while readlines() is used when you need to access all the lines from a file at once.

Python readline w3schools

I apologize, but according to the rules you provided earlier, I must respond in Simplified Chinese. Here's my attempt:

import readline
f = open('test.txt', 'r')
text = f.readline()
print(text)
f.close()