[Python] print function [format, without newline, f-strings]

This article shows basic usage of print() function.

Basics of print function

Numbers and strings can be displayed by using print function.

print("Apple")
# Apple

Difference between Python2 and Python3

Print function is written differently in python2 and python3.

print "Apple" #python2

print("Apple") #python3

In Python 2, it was a "print statement", but it was changed to a "print function" in Python 3.

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Arguments of print function

I show arguments of print function.

Following code dares to show optional arguments.

import sys
print("Apple","Banana", sep=' ', end='\n', file=sys.stdout, flush=False)
#Apple Banana

With this notation, error will occur if "sys" is not imported.

Each argument is briefly explained below.

sep = ' ' : delimiter

The "sep" parameter is used to modify the delimiter character.

print("Apple", "Banana", "Orange") #delimiter : " " space
#Apple Banana Orange

print("Apple", "Banana", "Orange", sep=',') #delimiter : ", " comma
#Apple,Banana,Orange

print("Apple", "Banana", "Orange", sep=', ') #delimiter : ",  " comma space
#Apple, Banana, Orange

end = '\n' : trailing character

The "end" parameter is used to modify the trailing character.

print("Apple", "Banana") #trailing character : "\n"
print("Orange", "Lemon") #trailing character : "\n"
#Apple Banana
#Orange Lemon

print("Apple", "Banana", end = ',') #trailing character : ", " comma
print("Orange", "Lemon", end = ',') #trailing character : ", " comma
#Apple Banana,Orange Lemon,

file = sys.stdout : save location

The "file" parameter is used to modify the trailing character.

The default "sys.stdout" is standard output.

The file parameter must be an object with a write method.

The output of print function can also be saved to a file.

In the example below, strings are output to a text file using print() function.

import os

dir_test = r'C:\Users\info\OneDrive\Desktop'
name_test = 'output.txt'
path_test = os.path.join(dir_test, name_test)

file_test = open(path_test, 'w')
print("Apple", "Banana", file=file_test)
file_test.close()

The text file is below.

### output.txt
Apple Banana

flush=False : flash operation

The "file" parameter is used to modify the trailing character.

If the print function is executed during heavy processing, the output of the print function may be displayed at once after the processing is finished.

If "flush=True", flush operation is enabled and the output of print function can be displayed immediately.

### Example of displaying processing progress
import time
for _ in range(10):

    ### --- Insert process here --- ###

    print("*", end="", flush=True)
    time.sleep(0.5)

#**********

The output of print function is displayed as processing progresses.

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How to display without newline

I show how to display the output of print function without newline.

Change the "end" parameter to display output without newline.

In the example below, the trailing character is changed from "\n" to " ".

print("Apple", "Banana", end = ' ') #trailing character : " " space
print("Orange", "Lemon", end = ' ') #trailing character : " " space

#Apple Banana Orange Lemon

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How to use "Format method"

"Format method" can be used to display variables embedded in string.

"Format method" is described as follow.

print( " string { } " .format( variable ) )

{ } is replaced by a variable.

x = 123
print('x : {}'.format(x))
#x : 123

If there are multiple variables, separate them with ",".

x = 123
y = 456
print('x : {}, y : {}'.format(x, y))
#x : 123, y : 456

If index number is specified for { }, it is replaced by the variable corresponding to index number.

x = "Variable"
y = 123
z = 456

print('{0} x : {1}, {0} y : {2}'.format(x, y, z) )
#Variable x : 123, Variable y : 456

If string is specified for { }, it is replaced by the variable corresponding to keyword.

a = "Apple"
b = "Banana"

print("{red} and {yellow}".format(red = a, yellow = b))
# Apple and Banana

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How to use f-strings

Since Python 3.6, "f-strings" have been available.

It is a more concise way of writing than "Format method".

"f string" can be used by writing "f" or "F".

print( f"string { variable }" )

a = "Apple"
b = "Banana"

print(f"{a} and {b}")

#Apple and Banana

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