Template method

Regular Expressions in Python

Maria Eugenia Inzaugarat

Data Scientist

Template strings

Simpler syntax
Slower than f-strings
Limited: don't allow format specifiers
Good when working with externally formatted strings

Basic syntax

from string import Template

my_string = Template('Data science has been called $identifier')

my_string.substitute(identifier="sexiest job of the 21st century")

'Data science has been called sexiest job of the 21st century'

Substitution

Use many $identifier
Use variables

from string import Template
job = "Data science"
name = "sexiest job of the 21st century"

my_string = Template('$title has been called $description')

my_string.substitute(title=job, description=name)

'Data science has been called sexiest job of the 21st century'

Substitution

Use ${identifier} when valid characters follow identifier

my_string = Template('I find Python very ${noun}ing but my sister has lost $noun')

my_string.substitute(noun="interest")

'I find Python very interesting but my sister has lost interest'

Substitution

Use $$ to escape the dollar sign

my_string = Template('I paid for the Python course only $$ $price, amazing!')

my_string.substitute(price="12.50")

'I paid for the Python course only $ 12.50, amazing!'

Substitution

Raise error when placeholder is missing

favorite = dict(flavor="chocolate")

my_string = Template('I love $flavor $cake very much')

my_string.substitute(favorite)

Traceback (most recent call last):
KeyError: 'cake'

Substitution

favorite = dict(flavor="chocolate")
my_string = Template('I love $flavor $cake very much')

try:
    my_string.substitute(favorite) 
except KeyError:
      print("missing information")

missing information

Safe substitution

Always tries to return a usable string
Missing placeholders will appear in resulting string

favorite = dict(flavor="chocolate")
my_string = Template('I love $flavor $cake very much')

my_string.safe_substitute(favorite)

'I love chocolate $cake very much'

Which should I use?

str.format():
- Good to start with. Concepts apply to f-strings.
- Compatible with all versions of Python.
f-strings:
- Always advisable above all methods.
- Only suitable when working with modern versions of Python (3.6+).
Template strings:
- When working with external or user-provided strings

Let's practice!

Regular Expressions in Python