Resources

Make a long number readable

>>> "{:,}".format(12345678910)

12,345,678,910

Representing objects

Printing a string and using repr.

>>> print('abc')
abc
>>> print(repr('abc'))
'abc'

Printing using .format and !r.

>>> print('{}'.format('abc'))
abc
>>> print('{!r}'.format('abc'))
'abc'

Without using print, the value is quoted.

>>> '{}'.format('abc')
'abc'
>>> '{!r}'.format('abc')
"'abc'"

The repr function gives out which can be used to create a new object. So a string must be quoted.

>>> print(repr('abc'))
'abc'
>>> print(repr(123))
123
>>> print(repr(True))
True

For classes, the __repr__ might be set to exactly match the contents so a new instance be created, or it might be a summary. But it won’t be set by default.

From Python String Conversion 101: Why Every Class Needs a “repr” article.

class Foo:
    def __init__(self, color, mileage):
        self.color = color
        self.mileage = mileage

    def __repr__(self):
       return (f'{self.__class__.__name__}('
               f'{self.color!r}, {self.mileage!r})')

    def __str__(self):
        return f'a {self.color} foo'

Formatting styles

New style

'{} {}'.format(foo, bar)

'{0} {1}'.format(foo, bar)

'{foo} {bar}'.format(foo=foo, bar=bar)

Use f-strings in Python 3.6+.

f'{foo} {bar}'

Modifiers

Using repr.

'{0!r}'.format(foo)

Using ASCII

'{0!a}'.format(foo)

Alignment

Align left.

'{:10}'
'{:<10}'

Align right with padding.

'{:>10}'

Align center.

'{:^10}'

Format integer. Aligns right.

'{:4d}'.format(42)
# => '  42'

Round a float.

# Default to 7.6 values (7 total length and 6 after point).
'{:f}'.format(3.141592653589793)
# => '3.141593'

# Custom
'{:3.2f}'.format(3.141592653589793)
# => '3.14'

# Add padding.
'{:06.2f}'.format(3.141592653589793)
# => '003.14'

Old style

'%s  %s' % (foo, bar)

Debugging

logging.debug("User name: %s", name)

Template Strings

A simpler and less powerful mechanism, but it is recommended when handling format strings generated by users. Due to their reduced complexity template strings are a safer choice.

from string import Template


name = 'Elizabeth'
t = Template('Hey $name!')
t.substitute(name=name)
# => 'Hey Elizabeth!'

Resources

Truncate long string

import textwrap


textwrap.shorten("Hello  world!", width=12)
# => 'Hello world!'
textwrap.shorten("Hello  world!", width=11)
# > 'Hello [...]'
textwrap.shorten("Hello world", width=10, placeholder="...")
# => 'Hello...'

source

'{:.5}'.format('xylophone')
# => 'xylop'

Working with strings

Repeating strings

>>> '---'*10
'------------------------------'

>>> ['---']*10
['---', '---', '---', '---', '---', '---', '---', '---', '---', '---']

| >>> print(" | ".join(['---']*10)) |
| ----------- | ------------------- ||  |  |  |  |  |  |  |

Convert strings to markdown table

header = "a,b,c".split(',')
row = "1,2,3".split(",")

print(" | ".join(header))
print(" | ".join(['---']*len(header)))
print(" | ".join(row))

| a   | b   | c   |
| --- | --- | --- |
| 1   | 2   | 3   |
a b c
1 2 3

Convert strings to dict

header = "a,b,c".split(',')
row = "1,2,3".split(",")

row_dict = {k: v for k, v in zip(header, row)}

print(row_dict)
# {'a': '1', 'b': '2', 'c': '3'}

Hex color code

Convert integer to hex string

>>> hex(12525)
'0x30ed'

Remove prefix

>>> "{:x}".format(12525)
'30ed'

Left-pad with spaces

>>> "{:6x}".format(12525)
'  30ed'

Left-pad with zeroes

"{:06x}".format(12525)
'0030ed'

Use f-strings

>>> color_number = 12525
>>> f"{color_number:06x}"
'0030ed'

Hex to integer

>>> x = 0x30ed
>>> type(x)
<type 'int'>

Max for 6-digit hex code.

>> 0xffffff
16777215

Textwrap

Dedent

Remove common whitespace

text = textwrap.dedent("""\
    a
      b
    c
""")
print(text)

a
  b
c