3.7.0 (v3.7.0:1bf9cc5093, Jun 26 2018, 23:26:24) 
[Clang 6.0 (clang-600.0.57)]
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# String formatting

# So far, when we want to put different strings together, we usually
# concatenate them using +
s1 = 'This course is'
s2 = 'CSC120'
s1 + s2
'This course isCSC120'
# Annoying: we forget the space
s = s1 + ' ' + s2
s
'This course is CSC120'
# what if we also want a period at the end?
s = s1 + ' ' + s2 + '.'
s
'This course is CSC120.'
# what if we want to add another part to the string?
s3 = "and it's the best!"
s = s1 + ' ' + s2 + ' ' + s3'.'
Traceback (most recent call last):
  Python Shell, prompt 15, line 1
Syntax Error: invalid syntax: <string>, line 1, pos 31
s = s1 + ' ' + s2 + ' ' + s3 + '.'
s
"This course is CSC120 and it's the best!."

# The point is, this doesn't seem very efficient
# and there has to be a better way

# String Formatting
# Lets us define the constant parts of a string and then the
# parts the might change

s1
'This course is'
s2
'CSC120'
# s1 contains the constant part
# write out the constant part, and indicate the variable part with
# curcly brackets
s = 'This course is {}'
# use the str.format() method to add the variable part
s.format('CSC120')
'This course is CSC120'
# The variable part is inserted in place of the curly brackets
# The spaces are part of the constant portion of the string

# adding a period is much easier as well:
s = 'This course is {}.'
s.format('CSC120')
'This course is CSC120.'
# you can also do this all in one line with the literal
'This course is {}.'.format('CSC120')
'This course is CSC120.'

# What about multiple variable parts?
# Just add more curly brackets:
"This course is {} and it's the {}.".format('CSC120', 'the best!')
"This course is CSC120 and it's the the best!."
"This course is {} and it's {}.".format('CSC120', 'the best!')
"This course is CSC120 and it's the best!."
# curly brackets are filled in from left to right in the 
# same order as the arguments to format()

# You can also specify the order in the curly brackets
"This course is {0} and it's {1}.".format('CSC120', 'the best!')
"This course is CSC120 and it's the best!."
"This course is {1} and it's {0}.".format('CSC120', 'the best!')
"This course is the best! and it's CSC120."
"This course is {0} and it's {1}.  I love {0}.".format('CSC120', 'the best!')
"This course is CSC120 and it's the best!.  I love CSC120."

# Always use this for putting strings together!
s = 'This course is {}.'
s.format('CSC120')
'This course is CSC120.'
s
'This course is {}.'
s = 'different string'
s
'different string'