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format() method allows you format string in any way you want.

**Syntax**:
template.format(p1, p1, .... , k1=v1, k2=v2)

template is a string containing format codes, format() method uses it’s argument to substitute value for each format codes. For e.g

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>>> 'Sam has {0} red balls and {1} yellow balls'.format(12, 31) |

{0} and {1} are format codes. The format code {0} is replaced by the first argument of format() i.e 12 , while {1} is replaced by the second argument of format() i.e 31 .

**Expected Output**:

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Sam has 12 red balls and 31 yellow balls |

This technique is okay for simple formatting but what if you want to specify precision in floating point number ? For such thing you need to learn more about format codes. Here is the full syntax of format codes.

Syntax: {[argument_index_or_keyword]:[width][.precision][type]}

type can be used with format codes

Format codes | Description |
---|---|

d | for integers |

f | for floating point numbers |

b | for binary numbers |

o | for octal numbers |

x | for octal hexadecimal numbers |

s | for string |

e | for floating point in exponent format |

Following examples will make things more clear.

**Example 1**:

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>>> "Floating point {0:.2f}".format(345.7916732) |

Here we specify 2 digits of precision and f is used to represent floating point number.

**Expected Output**:

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Floating point 345.79 |

**
Example 2**:

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>>> import math >>> "Floating point {0:10.3f}".format(math.pi) |

Here we specify 3 digits of precision, 10 for width and f for floating point number.

**Expected Output**:

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Floating point 3.142 |

**Example 3**:

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"Floating point pi = {0:.3f}, with {1:d} digit precision".format(math.pi, 3) |

here d in {1:d} represents integer value.

**Expected Output**:

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Floating point pi = 3.142, with 3 digit precision |

You need to specify precision only in case of floating point numbers if you specify precision for integer ValueError will be raised.

**Example 5**:

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'Sam has {1:d} red balls and {0:d} yellow balls'.format(12, 31) |

**Expected Output**:

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Sam has 31 red balls and 12 yellow balls |

**Example 6**:

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"In binary 4 is {0:b}".format(4) # b for binary, refer to Fig 1.1 |

**Expected Output**:

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In binary 4 is 100 |

**Example 7**:

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array = [34, 66, 12] "A = {0}, B = {1}, C = {2}".format(*array) |

**Expected Output**:

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'A = 34, B = 66, C = 12' |

**Example 8**:

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d = { 'hats' : 122, 'mats' : 42 } |

**Expected Output**:

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"Sam had {hats} hats and {mats} mats".format(**d) |

format() method also supports keywords arguments.

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'Sam has {red} red balls and {green} yellow balls'.format(red = 12, green = 31) |

Note while using keyword arguments we need to use arguments inside {} not numeric index.

**You can also mix position arguments with keywords arguments**

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'Sam has {red} red balls, {green} yellow balls \ and {0} bats'.format(3, red = 12, green = 31) |

format() method of formatting string is quite new and was introduced in python 2.6 . There is another old technique you will see in legacy codes which allows you to format string using % operator instead of format() method.

Let’s take an example.

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"%d pens cost = %.2f" % (12, 150.87612) |

Here we are using template string on the left of % . Instead of {} for format codes we are using % . On the right side of % we use tuple to contain our values. %d and %.2f are called as format specifiers, they begin with % followed by character that represents the data type. For e.g %d format specifier is a placeholder for a integer, similarly %.2f is a placeholder for floating point number.

So %d is replaced by the first value of the tuple i.e 12 and %.2f is replaced by second value i.e 150.87612 .

**Expected Output**:

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12 pens cost = 150.88 |

Some more examples

**Example 1**:

**New**:
"{0:d} {1:d} ".format(12, 31)

**Old**:
"%d %d" % (12, 31)

**Expected Output**:

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12 31 |

**Example 2**:

New: "{0:.2f} {1:.3f}".format(12.3152, 89.65431)

Old "%.2f %.3f" % (12.3152, 89.65431)

**Expected Output**:

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12.32 89.654 |

**Example 3**:

New: "{0:s} {1:o} {2:.2f} {3:d}".format("Hello", 71, 45836.12589, 45 )

Old: "%s %o %.2f %d" % ("Hello", 71, 45836.12589, 45 )

**Expected Output**:

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Hello 107 45836.13 45 |

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