[Basic] The ‘Pythonic’ Python Tutorial!

[DeaD_EyE]

https://github.com/the-machine-preacher/...iles.ipynb

In Cell 8:

with open('Examples/how_many_lines.txt') as lines_doc:
    for line in lines_doc.readlines():
        print(line)

It should be:

with open('Examples/how_many_lines.txt') as lines_doc:
    for line in lines_doc:
        print(line)

The example from Cell 8 opens the file,
then it iterates over all lines with readlines().
The list object is created in memory and holds the complete content of the file.

The correction of it, don't use readlines().
Iterating over a file, yields line by line without loading the whole content into memory.
The first function could not process a file, which is bigger as your RAM + Swap.


Another cool trick is the use of itertools.islice.
If you want to print the first 10 lines:

from itertools import islice


def head(file, lines):
    with open(file) as fd:
        for line in islice(fd, 0, lines):
            print(line.strip())


head(r'C:\Windows\system.ini', 10)

Tail have to be implemented different.

from collections import deque                
                                             
                                             
def tail(file, lines):                       
    result = deque(maxlen=lines)             
    with open(file) as fd:                   
        for line in fd:                      
            result.append(line.strip())      
    for line in result:                      
        print(line)                          

                                    
tail(r'C:\Windows\system.ini', 10)           

This is not optimal, because it has to read the whole file content.