print() in python

In this post, I will talk about about the print() statement and it's parameters.

So, I was experimenting with the help() function in python and tried the following command:

>>> help(print)
Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file:  a file-like object (stream); defaults to the current sys.stdout.
    sep:   string inserted between values, default a space.
    end:   string appended after the last value, default a newline.
    flush: whether to forcibly flush the stream.

me, after seeing file and flush arguments in the output:

I knew about the sep and end parameters but not about the other 2 parameters. But what are these unpopular-parameters-that-online-tutorials-do-not-talk-about?

Today, I am going to share what they are. But before that, let me explain what the first 2 parameters are.

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• sep is the string that is inserted between 2 values. For example:

>>> print(1, 2, 3, sep='-')
1-2-3
>>> print(1, 2, 3) # The default value of "sep" is a space
1 2 3

• end is the string that is appended after the last value. For example:

print(1, 2, 3, end='-')
print(4, 5, 6) # The default value of "end" is a newline
print("Hello")

Will print:

1 2 3-4 5 6
Hello

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Now that I have explained what sep and end are, let's talk about the 3rd parameter. The 3rd parameter is file.

It is a file-like object (stream). The default value of file is sys.stdout (sys is a built-in module). If you don't pass this argument, it will default to stdout and the output will be printed to the standard output. It is the terminal where you execute your code. Standard output is full for stdout (Python is implemented in C that's the reason we get to see stdout in Python). If you specify a value for file, the output will be printed to that file. For example:

print(1, 2, 3, sep="\n", file=open("output.txt", "w+"))

the open("output.txt", "w+") will create a file called output.txt (if it doesn't exist already) and write the output to it. So our output.txt file will look like this:

1
2
3

This allows us to write to a file directly without having to convert to a string. It also allows us to use the sep and end parameters of the print() function without worrying about how to implement them.

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Finally, let's talk about the flush parameter. The flush parameter is a boolean value. It "flushes" the internal buffer/stream. Let's see a small example for better understanding:

from time import sleep

# output is not flushed here
print("Hello", end=', ')
sleep(5)
print("world!")

would result in:

Hello, world!

The output looks perfect but there is the problem: the 5-second pause that was supposed to happen between the 2 words! It is not there. Now we run the same code but this time, we clear the output stream:

from time import sleep

# output is flushed this time
print("Hello", end=', ' flush=True)
sleep(5)
print("world!")

Now, when you run the program "Hello, " will be printed first and then after 5 seconds "world!" will be printed.

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That's all for this time.