How do you replace a variable in a string in python?

In this tutorial, we will learn about the Python replace() method with the help of examples.

The replace() method replaces each matching occurrence of the old character/text in the string with the new character/text.

Example

text = 'bat ball'

# replace b with c
replaced_text = text.replace('b', 'c')
print(replaced_text)

# Output: cat call

replace() Syntax

It's syntax is:

str.replace(old, new [, count]) 

replace() Parameters

The replace() method can take maximum of 3 parameters:

• old - old substring you want to replace
• new - new substring which will replace the old substring
• count (optional) - the number of times you want to replace the old substring with the new substring

Note: If count is not specified, the replace() method replaces all occurrences of the old substring with the new substring.

replace() Return Value

The replace() method returns a copy of the string where the old substring is replaced with the new substring. The original string is unchanged.

If the old substring is not found, it returns the copy of the original string.

Example 1: Using replace()

song = 'cold, cold heart'

# replacing 'cold' with 'hurt'
print(song.replace('cold', 'hurt'))

song = 'Let it be, let it be, let it be, let it be'

# replacing only two occurences of 'let'
print(song.replace('let', "don't let", 2))

Output

hurt, hurt heart
Let it be, don't let it be, don't let it be, let it be

More Examples on String replace()

song = 'cold, cold heart'
replaced_song = song.replace('o', 'e')

# The original string is unchanged
print('Original string:', song)

print('Replaced string:', replaced_song)

song = 'let it be, let it be, let it be'

# maximum of 0 substring is replaced
# returns copy of the original string
print(song.replace('let', 'so', 0))

Output

Original string: cold, cold heart
Replaced string: celd, celd heart
let it be, let it be, let it be

I'm trying to maintain/update/rewrite/fix a bit of Python that looks a bit like this:

variable = """My name is %s and it has been %s since I was born.
              My parents decided to call me %s because they thought %s was a nice name.
              %s is the same as %s.""" % (name, name, name, name, name, name)

There are little snippets that look like this all over the script, and I was wondering whether there's a simpler (more Pythonic?) way to write this code. I've found one instance of this that replaces the same variable about 30 times, and it just feels ugly.

Is the only way around the (in my opinion) ugliness to split it up into lots of little bits?

variable = """My name is %s and it has been %s since I was born.""" % (name, name)
variable += """My parents decided to call me %s because they thought %s was a nice name.""" % (name, name)
variable += """%s is the same as %s.""" % (name, name)

mdeous

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asked Aug 8, 2011 at 13:36

Use a dictionary instead.

var = '%(foo)s %(foo)s %(foo)s' % { 'foo': 'look_at_me_three_times' }

Or format with explicit numbering.

var = '{0} {0} {0}'.format('look_at_meeee')

Well, or format with named parameters.

var = '{foo} {foo} {foo}'.format(foo = 'python you so crazy')

answered Aug 8, 2011 at 13:39

Cat Plus PlusCat Plus Plus

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1

Use formatting strings:

>>> variable = """My name is {name} and it has been {name} since..."""
>>> n = "alex"
>>>
>>> variable.format(name=n)
'My name is alex and it has been alex since...'

The text within the {} can be a descriptor or an index value.

Another fancy trick is to use a dictionary to define multiple variables in combination with the ** operator.

>>> values = {"name": "alex", "color": "red"}
>>> """My name is {name} and my favorite color is {color}""".format(**values)
'My name is alex and my favorite color is red'
>>>

answered Aug 8, 2011 at 13:47

monkutmonkut

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1

Python 3.6 has introduced a simpler way to format strings. You can get details about it in PEP 498

>>> name = "Sam"
>>> age = 30
>>> f"Hello, {name}. You are {age}."
'Hello, Sam. You are 30.'

It also support runtime evaluation

>>>f"{2 * 30}"
'60'

It supports dictionary operation too

>>> comedian = {'name': 'Tom', 'age': 30}
>>> f"The comedian is {comedian['name']}, aged {comedian['age']}."
 The comedian is Tom, aged 30.

answered Jun 22, 2019 at 5:22

Arghya SahaArghya Saha

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Use the new string.format:

name = 'Alex'
variable = """My name is {0} and it has been {0} since I was born.
          My parents decided to call me {0} because they thought {0} was a nice name.
          {0} is the same as {0}.""".format(name)

answered Aug 8, 2011 at 13:39

Zaur NasibovZaur Nasibov

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>>> "%(name)s %(name)s hello!" % dict(name='foo')
'foo foo hello!'

answered Aug 8, 2011 at 13:39

Mikhail KorobovMikhail Korobov

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You could use named parameters. See examples here

answered Aug 8, 2011 at 13:38

J0HNJ0HN

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variable = """My name is {0} and it has been {0} since I was born.
              My parents decided to call me {0} because they thought {0} was a nice name.
              {0} is the same as {0}.""".format(name)

answered Aug 8, 2011 at 13:39

xubuntixxubuntix

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answered Aug 8, 2011 at 13:38

GryphiusGryphius

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If you are using Python 3, than you can also leverage, f-strings

myname = "Test"
sample_string = "Hi my name is {name}".format(name=myname)

to

sample_string = f"Hi my name is {myname}"

answered Feb 28, 2020 at 13:35

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