Replace a python string using format function

Question

I have a string which gets replaced in the backend code. ${} indicates that the string pattern is to be replaced. Example -

I am going to ${location} for ${days}

I have a dict with values to be replaced below. I want to find if ${location} is present in the text and replace it with the key value in str_replacements. Below is my code. The string replacement does not work using .format. It works using %s but i do not want to use it.

text = "I am going to ${location} for ${days}"
str_replacements = {
    'location': 'earth',
    'days': 100,
    'vehicle': 'car',
}

for key, val in str_replacements.iteritems():
    str_to_replace = '${{}}'.format(key)
    # str_to_replace returned is ${}. I want the key to be present here.
    # For instance the value of str_to_replace needs to be ${location} so
    # that i can replace it in the text
    if str_to_replace in text:
        text = text.replace(str_to_replace, val)

I do not want to use %s to substitute the string. I want to achieve the functionality with .format function.

Can you control the format on the backend? Do you need the $s? Why not just directly use the format that .format expects? — Karl Knechtel
– Karl Knechtel, Commented Oct 7, 2020 at 6:05

Rakesh · Accepted Answer · 2020-10-07 05:55:01Z

2

Use an extra {}

Ex:

text = "I am going to ${location} for ${days}"
str_replacements = {
    'location': 'earth',
    'days': 100,
    'vehicle': 'car',
}

for key, val in str_replacements.items():
    str_to_replace = '${{{}}}'.format(key)
    if str_to_replace in text:
        text = text.replace(str_to_replace, str(val))
print(text)
#  -> I am going to earth for 100

answered Oct 7, 2020 at 5:55

Rakesh

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Jan · Accepted Answer · 2020-10-07 05:59:17Z

1

You could use a small regular expression instead:

import re

text = "I am going to ${location} for ${days} ${leave_me_alone}"
str_replacements = {
    'location': 'earth',
    'days': 100,
    'vehicle': 'car',
}

rx = re.compile(r'\$\{([^{}]+)\}')

text = rx.sub(lambda m: str(str_replacements.get(m.group(1), m.group(0))), text)
print(text)

This would yield

I am going to earth for 100 ${leave_me_alone}

answered Oct 7, 2020 at 5:59

Jan

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Comments

Jack Daniel · Accepted Answer · 2020-10-07 06:04:09Z

0

You can do it in two ways:

Parameterised - Order of parameters is not followed strictly
Non Parametrised - Order of parameters is not followed strictly

Example as follows:

answered Oct 7, 2020 at 6:04

Jack Daniel

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