Python Formatted Output (% and format Usage)

Integer Output

• %o—Octal (Base 8)
• %d—Decimal (Base 10)
• %x—Hexadecimal (Base 16)

Floating-Point (Decimal) Output

Formatted Output

>>> awsl = 2.333
>>> print('%f' % awsl)  # Default to 6 decimal places
2.333000
>>> print('%.1f' % awsl)  # Round to 1 decimal place
2.3
>>> print('%e' % awsl)  # Scientific notation, 6 decimal places by default
2.333000e+00
>>> print('%.2e' % awsl)  # Scientific notation, 2 decimal places
2.33e+00
>>> print('%g' % 2.3333333)  # Up to 6 significant figures
2.33333
>>> print('%.5g' % 233.33333)  # 5 significant figures
233.33
>>> print('%.2g' % 2333.3333)  # 2 significant figures, auto scientific notation
2.3e+03

Built-in round()

round(number[, ndigits])

• Parameters:
  • number: The number to round.
  • ndigits: The number of decimal places to round to. Defaults to 0.
• Return Value: The rounded value of number to ndigits decimal places.
• If round() is called with a single argument, it rounds to the nearest integer.
• When a specific decimal place is specified, the function usually follows standard rounding rules.
• Special case: When rounding .5, Python rounds to the nearest even number.

Note:.5 rounding behavior can be tricky, and round() may yield different results between Python 2 and Python 3. Avoid relying on it in critical applications.

>>> round(1.1125)  # Round to nearest integer
1
>>> round(1.1135, 3)  # Round to 3 decimal places; 3 is odd, so round down
1.113
>>> round(1.1125, 3)  # Round to 3 decimal places; 2 is even, so round up
1.113
>>> round(2.675, 2)  # Round to 2 decimal places
2.67

Explanation of round(2.675, 2) Result: Although the result seems incorrect (2.67 instead of 2.68), this behavior arises from floating-point precision. Internally, the binary representation of 2.675 is slightly less than the actual value, causing it to round to 2.67.

String Output

• %s
• %10s—Right-aligned, occupying 10 spaces
• %-10s—Left-aligned, occupying 10 spaces
• %.2s—Extract 2 characters
• %10.2s—Right-aligned, occupying 10 spaces, extract 2 characters

>>> print('%s' % 'hello world')  # String output
hello world
>>> print('%20s' % 'hello world')  # Right-aligned, 20 spaces
         hello world
>>> print('%-20s' % 'hello world')  # Left-aligned, 20 spaces
hello world         
>>> print('%.2s' % 'hello world')  # Extract 2 characters
he
>>> print('%10.2s' % 'hello world')  # Right-aligned, extract 2 characters
        he
>>> print('%-10.2s' % 'hello world')  # Left-aligned, extract 2 characters
he

Outputting Multiple Variables

>>> hhh = 2333
>>> awsl = 2.333
>>> print('%d + %f = %f' % (hhh, awsl, hhh + awsl))
2333 + 2.333000 = 2335.333000

Comprehensive List of Format Specifiers

Symbol	Description
%c	Character or ASCII value
%s	String
%d	Integer
%u	Unsigned integer
%o	Unsigned octal
%x	Unsigned hexadecimal (lowercase)
%X	Unsigned hexadecimal (uppercase)
%f	Floating-point number with specified precision
%e	Scientific notation (lowercase 'e')
%E	Scientific notation (uppercase 'E')
%g	Compact representation of float (removes trailing zeros)
%G	Similar to %g with uppercase letters for scientific notation
%p	Pointer (memory address in hexadecimal)

Auxiliary Instructions for Formatting Operators:

Symbol	Description
*	Defines width or decimal precision
-	Used for left alignment
+	Displays a plus sign (+) before positive numbers
	Displays a space before positive numbers
#	Prefixes octal numbers with '0' and hexadecimal numbers with '0x' or '0X' (depending on whether 'x' or 'X' is used)
0	Pads numbers with zeros instead of spaces
%	Outputs a single '%' with '%%'
(var)	Maps variables (dictionary arguments)
m.n.	m specifies the minimum total width, and n specifies the number of decimal places (if applicable)

Using format

Compared to basic formatted output with %, the format() function is more powerful. It treats strings as templates and formats them using the parameters passed, with {} used as placeholders instead of %.

Positional Matching

1. Without an index, i.e., {}.
2. With numbered indices, allowing reordering, i.e., {1}, {2}.
3. With keywords, i.e., {a}, {tom}.

>>> print('{} {}'.format('zeruns', 'blog.zeruns.com'))  # No index
zeruns blog.zeruns.com
>>> print('{0} {1}'.format('hello', 'world'))  # With numbered indices
hello world
>>> print('{1}{0}'.format('blog.zeruns.com', 'https://'))
https://blog.zeruns.com
>>> print('{0} {1} {0}'.format('hello', 'world'))  # Reordered
hello world hello
>>> print('{1} {1} {0}'.format('hello', 'world'))
world world hello
>>> print('{a} {tom} {a}'.format(tom='hello', a='world'))  # With keywords
world hello world

# Using positional matching
>>> '{0}, {1}, {2}'.format('a', 'b', 'c')
'a, b, c'
>>> '{}, {}, {}'.format('a', 'b', 'c')  # Supported in Python 3.1+
'a, b, c'
>>> '{2}, {1}, {0}'.format('a', 'b', 'c')
'c, b, a'
>>> '{2}, {1}, {0}'.format(*'abc')  # Can reorder
'c, b, a'
>>> '{0}{1}{0}'.format('abra', 'cad')  # Can repeat
'abracadabra'

# Using name matching
>>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W')
'Coordinates: 37.24N, -115.81W'
>>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'}
>>> 'Coordinates: {latitude}, {longitude}'.format(**coord)
'Coordinates: 37.24N, -115.81W'

# Matching parameters by index or key
>>> coord = (3, 5)
>>> 'X: {0[0]};  Y: {0[1]}'.format(coord)
'X: 3;  Y: 5'
>>> a = {'a': 'test_a', 'b': 'test_b'}
>>> 'X: {0[a]};  Y: {0[b]}'.format(a)
'X: test_a;  Y: test_b'