string-formatting.md

String formatting in Python

F-strings (Python >=3.6)

F-strings are faster than the other string formatting methods and are easier to read and use. Here are some tricks you may not have known.

name = "Test"
f'My app name is {name}.'  # 'My app name is Test.

1. Number formatting:

You can do various formatting with numbers.

number = 150

# decimal places to n -> .nf
print(f"number: {number:.2f}")
# number: 150.00

# hex conversion
print(f"hex: {number:#0x}")
# hex: 0x96

# binary conversion
print(f"binary: {number:b}")
# binary: 10010110

# octal conversion
print(f"octal: {number:o}")
# octal: 226

# scientific notation
print(f"scientific: {number:e}")
# scientific: 1.500000e+02

# total number of characters
print(f"Number: {number:09}")
# Number: 000000150

ratio = 1 / 2
# percentage with 2 decimal places
print(f"percentage = {ratio:.2%}")
# percentage = 50.00%

2. Stop writing print(f”var = {var}”)

This is the debug feature with f-strings.

a, b = 5, 15
print(f"a = {a}") # Doing this ?
# a = 5

# Do this instead.
print(f"{a = }")
# a = 5

# Arithmatic operations
print(f"{a + b = }")
# a + b = 20

# with formatting
print(f"{a + b = :.2f}")
# a + b = 20.00

3. Date formatting

You can do strftime() formattings from f-string.

import datetime

today = datetime.datetime.now()
print(f"datetime : {today}")
# datetime : 2023-10-27 11:05:40.282314

print(f"date time: {today:%m/%d/%Y %H:%M:%S}")
# date time: 10/27/2023 11:05:40

print(f"date: {today:%m/%d/%Y}")
# date: 10/27/2023

print(f"time: {today:%H:%M:%S %p}")
# time: 11:05:40 AM

Old method (Python >=2.6)

'{} {}'.format('one', 'two')  # Output: 'one two'
'{} {}'.format(1, 2)  # Output: '1 2'

Very old method

'%s %s' % ('one', 'two')  # Output: 'one two'
'%d %d' % (1, 2)  # Output: '1 2'

Number formatting

The following table shows various ways to format numbers using str.format(), including examples for both float formatting and integers.

To run examples use print("FORMAT".format(NUMBER)). So to get the output of the first example, you would run: print("{:.2f}".format(3.1415926)).

Number	Format	Output	Description
3.1415926	{:.2f}	3.14	2 decimal places
3.1415926	{:+.2f}	+3.14	2 decimal places with sign
-1	{:+.2f}	-1.00	2 decimal places with sign
2.71828	{:.0f}	3	No decimal places
5	{:0>2d}	05	Pad number with zeros (left padding, width 2)
5	{:x<4d}	5xxx	Pad number with x’s (right padding, width 4)
10	{:x<4d}	10xx	Pad number with x’s (right padding, width 4)
1000000	{:,}	1,000,000	Number format with comma separator
0.25	{:.2%}	25.00%	Format percentage
1000000000	{:.2e}	1.00e+09	Exponent notation
13	{:10d}	13	Right aligned (default, width 10)
13	{:<10d}	13	Left aligned (width 10)
13	{:^10d}	13	Center aligned (width 10)