String Formatting (% Operator)#

Note

Prefer f-strings The % formatting operator is a legacy approach. In modern Python (3.6+), f-strings are the preferred method for string formatting. See Strings for details on f-strings.

The % operator allows you to embed values inside a string using conversion specifications.

Syntax#

"format string" % (values)

name = "Alice"
age = 30
print("Name: %s, Age: %d" % (name, age))
# Name: Alice, Age: 30

Conversion Specification Pattern#

%[flags][width][.precision]code

Each % placeholder in the string follows this pattern.

Conversion Codes#

Code	Description	Example
`%s`	String (or any object via `str()`)	`"%s" % "hello"` → `"hello"`
`%d` or `%i`	Integer (decimal)	`"%d" % 42` → `"42"`
`%f`	Floating-point (default 6 decimals)	`"%f" % 3.14` → `"3.140000"`
`%e`	Floating-point in scientific notation	`"%e" % 0.001` → `"1.000000e-03"`
`%c`	Single character (int or str)	`"%c" % 65` → `"A"`

Flags#

Flag	Description	Example
`-`	Left-align within the field width	`"%-10s!"` → `"hello !"`
`+`	Show sign for positive numbers	`"%+d" % 42` → `"+42"`
(space)	Insert space before positive numbers	`"% d" % 42` → `" 42"`
`#`	Alternate form (`0x` for hex, `0o` for octal)	`"%#x" % 255` → `"0xff"`
`0`	Zero-pad numbers	`"%05d" % 42` → `"00042"`

Width#

Minimum number of characters in the output. Pads with spaces (or zeros if 0 flag is used).

print("%10s" % "hi")    #         hi  (right-aligned, 10 chars wide)
print("%-10s!" % "hi")  # hi        !  (left-aligned)
print("%10d" % 42)      #         42

Precision#

For floats, specifies the number of decimal places. For strings, specifies the maximum length.

print("%.2f" % 3.14159)   # 3.14
print("%.4f" % 3.14159)   # 3.1416
print("%.3s" % "hello")   # hel

Combined Examples#

# Right-aligned float with 2 decimal places, 8 chars wide
print("%8.2f" % 3.14159)    #     3.14

# Zero-padded integer, 5 chars wide
print("%05d" % 42)          # 00042

# Multiple values
x, y = 10.5, 20.3
print("Point: (%.1f, %.1f)" % (x, y))  # Point: (10.5, 20.3)

# Dictionary-based formatting
data = {"name": "Alice", "score": 95.5}
print("%(name)s scored %(score).1f%%" % data)  # Alice scored 95.5%