File

In this lecture, we'll learn how to treat the files in Python.
To access the files from Python code, you should use open function. When opening a file, you need to specify the mode.

You can choose text or binary mode after the r, w, a character by specifying t or b. Text mode is used by default.

open

You need to open the file anyway.

f = open("filename.txt", "r")  # read
f = open("filename.txt", "w")  # write
f = open("filename.txt", "a")  # append

To read the file, read function can be used.

f = open("test.txt", "r")
lines = f.read()

However, read gives the whole file in one string, so not very useful for the file with multiple lines (which is usual).

Instead, use readlines

f = open("test.txt", "r")
lines = f.readlines()

You can write to file with write function.

f = open("test.txt", "w")
f.write("The first comment.\n")
f.close()

Note that w mode will overwrite the file. If you want append to a file, use the append mode a.

After accessing the file, you should close the file.
```
f = open("filename.txt", "w")
f.close()
```

You can use with statement to open the file, and in this way, you can omit the closing procedure of the file.
```
with open("test.txt", "w") as f:
    f.write("Some string\n")
```

reading text file

with open("textfile.txt", "r") as f:
    for line in f:
        line = line.strip()
        print(line)

The with statement works with any "context manager" that needs setup/cleanup. For example, in PyTorch:

import torch

# Disable gradient computation during inference
with torch.no_grad():
    output = model(input)