LPTHW - Exercise 6: Strings Text

LPTHW - Exercise 6

More working with strings and text in this exercise.

Having looked into string formatting in the last exercise I realised that I was looking into something quite a bit further on in the course than I needed to right now.

x = "There are {!a} types of people.".format(10)
binary = "binary"
do_not = "don't"
y = f"Those who know {binary} and those who {do_not}."


print(f"I said: {x!r}")
print(f"I also said: '{y}'")

hilarious = False
joke_evaluation = "Isn't that joke so funny?! {}"


w = "This is the left side of..."
e = "a string with a right side."

print(w + e)

Learn Python The Hard Way Study Drills

1. Go through this program and write a comment above each line explaining it.

# Sets variable x to string with an embedded format string. Format strings 
# are way to insert (embed) a thing within a string such that the final 
# output will include the thing or whatever operation the thing is part of.
x = "There are {!a} types of people.".format(10)

# sets variable 'binary' to 'binary' = redundant slightly but needed
binary = "binary"

# sets variable 'do_not' to 'don't'
do_not = "don't"

# Sets variable y to string with two embedded format strings 
# (binary and do_not)
y = "Those who know {binary} and those who {do_not}."


# Print the RAW output of the x variable inside the string 
# (that's what !r does) So x get's printed with quotes around it even 
# though not specificed in this string. Also, Notice how the format string 
# from x also caries through to this string. Format strings seem to cascade 
# and output through levels of strings. 
print("I said: {x!r}")

# Output string with called variable but not output RAW so needs quotes 
# around format string to display in output. If you don't specify a conversion
# flag the `__format__()` method for that value will do the formatting - 
# I think this means if you insert digits it'll format as digits, 
# text as a string etc.
print "I also said:'{y}'."

hilarious = False
joke_evaluation = "Isn't that joke so funny?! {!r}"

# Here you learn that you can set the content of the format string 'later' 
# by creating the format string in one variable yet specifying it's 
# 'content/operator' at print time. Here the variable 'hilarious' is set as 
# the format string at print time, which will output False in the final print. 
# This seems powerful behaviour. 

# Shows that you can add variables together. This just literally seems to 
# concantenate the two together rather than any mathematical operation. 
# Yep, + concantenates strings. Don't use + to concantenate more than 2 
# strings though as this is highly inefficient. 
# Instead use ''.join e.g ''.join((w,e))
w = "This is the left side of..."
e = "a string with a right side."
print w + e

# Test of ''.join
print ''.join((w,e))

There are a few subtle things to look at here. Look into .format() and that syntax as it's from previous versions of Python 3. Also look into the use of {!r} and {!s}. These are conversion flags and details of these can be found in the docs.

Incidentally, this StackOverflow question has some interesting and useful explanations concerning the difference between %r and %s.

Yes, those example deal with the Python 2 syntax, but you can use the principles in Python 3 as the syntax has simply changed to {!r} and {!s} respectively.

2. Find all the places where a string is put inside a string. There are four places.

There are technically 3 %s included in the exact example, but also two %r that output strings to, so you could say there were either 3 or 5, but not 4.

EDIT: I just took another look. You could say 4 but you could actually say 6.

Lets run through it:

1 and 2 occur when print y is called at line 11. Two variables, themselves strings, are called in a string.

3 occurs on line 14 where variable x (itself a string) is called within a string.

4 occurs on line 16 where variable y is called.


line 16 calls that variable y, which itself is a string within a string, so you get 2 strings called within a string within a string.

So you can say the technical answer to the question is indeed 4 or you could say that it's 6 thanks to the string within a string within a string.


3. Are you sure there are only four places? How do you know? Maybe I like lying.

Could be 6. See above.

4. Explain why adding the two strings w and e with + makes a longer string.

Adding strings concatenates them, literally joining them together. This isn't the most efficient way to 'join' strings and would slow you're programme down if used to join many strings. The proper method is to use ''.join().

More info and examples on ''.join()

Source files

As ever, source files on GitHub

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