Test & Debug Tips: Create a file of the specified size in Python

Introduction

This is a trick that can be used for testing and debugging. Want to create a large file with random content for testing? .. Moreover, it is instant.

Create a huge file "instantly" on one command line

Create a 1024 byte file

`Execution example (creating a 1024-byte file)`


C:\>python -c "import sys; import numpy; sys.stdout.buffer.write(numpy.random.bytes(1024));" > 1024.bin

Create a 1MB file

`Execution example (1MB/1,048,576 byte file creation)`


C:\>python -c "import sys; import numpy; sys.stdout.buffer.write(numpy.random.bytes(1048576));" > 1048576.bin

Create a 1GB file

`Execution example (1MB/1,073,741,824-byte file creation)`


python -c "import sys; import numpy; sys.stdout.buffer.write(numpy.random.bytes(1073741824));" > 1073741824.bin

It took about 1 minute to create a 1GB file with Core i7-5500U-2.4GHz/SSD-DISK. (If you want a zero-padded file, please use fsutil. It will be finished in an instant)

See the result

`Execution result`


C:\work>dir
2021/01/11  10:00             1,024 1024.bin
2021/01/11  10:08         1,048,576 1048576.bin
2021/01/12  19:28     1,073,741,824 1073741824.bin

Summary

I posted a method to realize it instantly only on the command line. I hope it helps you when you are busy.

bonus

An error occurs with sys.stdout.write ()

Execution example that causes an error

>>> sys.stdout.write(numpy.random.bytes(1024))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: write() argument must be str, not bytes

I got an error when I tried to output. The part-time job is useless. I thought it was okay because numpy.random.bytes is returned as a string type like "b'\ xe5'". ..

What is the type of sys.stdout?

C:\>python
>>> import sys;
>>> print(type(sys.stdout));
<class '_io.TextIOWrapper'>

The type of sys.stdout is'_io.TextIOWrapper'.

What is class'_io.TextIOWrapper'?

────────────────────────── class '_io.TextIOWrapper' A buffered text stream providing higher-level access to a BufferedIOBase buffered binary stream. It inherits TextIOBase. (** Inherit TextIOBase **) ────────────────────────── '_io.TextIOWrapper' was a class for text processing. ** I have no choice but to look for a byte interface **. It is said to inherit'TextIOBase'.

What is class io.TextIOBase?

────────────────────────── class io.TextIOBase Base class for text streams. This class provides a character and line based interface to stream I/O. It inherits IOBase. There is no public constructor. ────────────────────────── This class had a member called buffer that accessed the binary IF.

What is io.TextIOBase.buffer (sys.stdout.buffer)?

────────────────────────── buffer The underlying binary buffer (BufferedIOBase instance) that TextIOBase handles. ────────────────────────── It seems that you can use buffer for binary output.