Python println()? Differences from print() and Usage Guide

1. Introduction

2. Python’s print() function

Basic usage of the print() function

print("Hello, World!")

Hello, World!

Printing multiple strings at once

print("Hello", "Python", "World")

Hello Python World

Output using variables

name = "Alice"
age = 25
print("Name:", name, "Age:", age)

Name: Alice Age: 25

Features of the print() function

• Can display strings and numbers to standard output.
• When multiple arguments are passed, they are separated by spaces.
• By default, it adds a newline (configurable).

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3. Differences between Java’s println() and Python’s print()

How to use Java’s println()

System.out.println("Hello, World!");

System.out.print("Hello");
System.out.print(" World");

Hello World

Differences with Python’s print()

print("Hello", end="")
print(" World")

Hello World

Comparison table of standard output in Java and Python

4. print() Function Applications

4.1 Outputting Multiple Values with print()

Example</4>

print("Python", "is", "awesome")

Python is awesome

age = 25
print("I am", age, "years old")

I am 25 years old

4.2 String Formatting with <codeprint()

(1) Using the format() method

name = "Alice"
age = 25
print("Name: {}, Age: {}".format(name, age))

Name: Alice, Age: 25

(2) f-strings (recommended for Python 3.6 and later)

name = "Alice"
age = 25
print(f"Name: {name}, Age: {age}")

Name: Alice, Age: 25

4.3 Preventing Newlines with print()

Example

print("Hello", end="")
print(" World")

Hello World

4.4 Changing the Separator with print()

Example

print("Python", "Java", "C++", sep=", ")

Python, Java, C++

4.5 Outputting to a File with print()

Example

with open("output.txt", "w") as f:
    print("This will be written to the file.", file=f)

4.6 Unbuffered (Real-Time) Output with print()

Example

import time

for i in range(5):
    print(i, end=" ", flush=True)
    time.sleep(1)

0 1 2 3 4

4.7 Capturing print() Output into a Variable (using sys.stdout)

Example

import sys
from io import StringIO

# Temporarily capture output
_stdout = sys.stdout
sys.stdout = mystdout = StringIO()

print("Captured output")

# Retrieve captured content
sys.stdout = old_stdout  # Restore original standard output
output = mystdout.getvalue()
print("Saved output:", output)

Saved output: Captured output

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5. print() Function Cautions and Best Practices

5.1 Cautions When Using the print() Function

(1) Large amounts of output can degrade performance

❌ Code to Avoid

for i in range(1000000):
    print(i)  # Very slow because it writes to standard output each time

✅ Improved Approach

output = "n".join(str(i) for i in range(1000000))
print(output)

(2) Don’t overuse print() for debugging

❌ Code to Avoid

print("Debug message: variable x =", x)

✅ Using the logging Module

import logging

logging.basicConfig(level=logging.DEBUG)
x = 10
logging.debug(f"Debug message: variable x = {x}")

(3) Explicitly Manage the Destination of print() Output

Saving Logs to a File

with open("log.txt", "w") as f:
    print("This log will be saved to a file", file=f)

5.2 Best Practices for the print() Function

(1) Leverage f-strings

❌ Code to Avoid

print("Name: " + name + ", Age: " + str(age))

✅ Improved Approach

print(f"Name: {name}, Age: {age}")

(2) Use the end Parameter to Prevent Unnecessary Newlines

❌ Code to Avoid

print("Processing...")
print("Done!")

✅ Improved Approach

print("Processing...", end="")  
print("Done!")

Processing...Done!

(3) Use the sep Parameter to Set Custom Separators

Example: comma-separated

print("Apple", "Banana", "Cherry", sep=", ")

Apple, Banana, Cherry

(4) Real-Time Output Processing (flush=True)

Example

import time

for i in range(3):
    print(f"Processing {i+1}/3...", end="r", flush=True)
    time.sleep(1)

Processing 1/3...
Processing 2/3...
Processing 3/3...

Summary

⚠ print() Function Cautions

• Large amounts of output can lead to performance degradation (using join() speeds it up)
• Don’t overuse it during debugging (using logging is easier to manage)
• Be aware of the output destination (you can use the file parameter to output to a file)

✅ print() Function Best Practices

• Use f-strings to simplify formatting
• Use end to prevent unnecessary newlines
• Use sep to customize output
• Use flush=True for real-time output

6. Frequently Asked Questions (FAQ) about the print() function

Q1: Does Python have a println function?

Python example

print("Hello, World!")  # Prints a newline by default

Java example

System.out.println("Hello, World!");  // Prints a newline by default

Q2: How to prevent a newline with the print() function?

Example

print("Hello", end="")
print(" World")

Hello World

Q3: Can you reproduce exactly the same behavior as Java’s println() in Python?

Example

print("Hello, World!", end="n")  # Explicit newline

Q4: How to output multiple variables with print()?

Example

name = "Alice"
age = 25
print("Name:", name, "Age:", age)

Name: Alice Age: 25

print(f"Name: {name}, Age: {age}")

Q5: How to write print() output to a file?

Example

with open("output.txt", "w") as f:
    print("This is the content that will be saved to the file", file=f)

Q6: How to write to standard output without using print()?

Example

import sys
sys.stdout.write("Hello, World!n")

Q7: Why do errors occur when using print()?

(1) TypeError: can only concatenate str (not "int") to str

print("Age: " + 25)  # Error!

print("Age: " + str(25))  # Correct usage

(2) SyntaxError: Missing parentheses in call to 'print'

print "Hello, World!"  # Python 2 syntax

print("Hello, World!")  # Correct usage

Q8: How to debug without using print()?

Example

import logging
logging.basicConfig(level=logging.DEBUG)

x = 42
logging.debug(f"Value of variable x: {x}")

7. Summary

7.1 Basics of Python’s print() function

• Python does not have a println() function; instead, you use the print() function.
• print() outputs with a newline by default.

  print("Hello, World!")  # newline after output

• Can output multiple values at once (space-separated)

  print("Python", "is", "awesome")

7.2 Differences between Java’s println() and Python’s print()

7.3 Advanced uses of the print() function

7.4 Caveats of the print() function

1. Large amounts of output can affect performance

   output = "n".join(str(i) for i in range(1000000))
   print(output)  # speed up by bulk output

2. For debugging, use logging instead of print()

   import logging
   logging.basicConfig(level=logging.INFO)
   logging.info("debug message")

3. When outputting elsewhere than standard output, use sys.stdout

   import sys
   sys.stdout.write("Hello, World!n")

7.5 FAQ Summary

7.6 Related topics to learn next

1. Log management using the logging module

   import logging
   logging.basicConfig(level=logging.INFO)
   logging.info("This is an INFO log")

2. Standard I/O (sys.stdin, sys.stdout, sys.stderr)

   import sys
   sys.stdout.write("Hello, World!n")

3. File I/O (how to use open())

   with open("output.txt", "w") as f:
       f.write("example of file output")

4. Python debugging techniques

   import pdb; pdb.set_trace()  # set breakpoint here

7.7 Summary

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