Exercise 12: Prompting People

When you typed raw_input() you were typing the ( and ) characters, which are parenthesis characters. This is similar to when you used them to do a format with extra variables, as in "%s %s" % (x, y). For raw_input you can also put in a prompt to show to a person so he knows what to type. Put a string that you want for the prompt inside the () so that it looks like this:

y = raw_input("Name? ")

This prompts the user with "Name?" and puts the result into the variable y. This is how you ask someone a question and get the answer.

This means we can completely rewrite our previous exercise using just raw_input to do all the prompting.

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age = raw_input("How old are you? ") height = raw_input("How tall are you? ") weight = raw_input("How much do you weigh? ") print "So, you're %r old, %r tall and %r heavy." % ( age, height, weight)

What You Should See

$ python ex12.py
How old are you?  38
How tall are you?  6'2"
How much do you weigh?  180lbs
So, you're '38' old, '6\'2"' tall and '180lbs' heavy.

=====================================================================

age = input("How old are you? ")
height = input("How tall are you? ")
weight = input("How much do you weigh? ")

print ("So, you're %r old, %r tall and %r heavy." % (
    age, height, weight))

>>> ==================== RESTART =======================

>>> 
How old are you? 18
How tall are you? 176
How much do you weigh? 76
So, you're '18' old, '176' tall and '76' heavy.
>>> 

Exercise 11: Asking Questions

Now it is time to pick up the pace. You are doing a lot of printing to get you familiar with typing simple things, but those simple things are fairly boring. What we want to do now is get data into your programs. This is a little tricky because you have to learn to do two things that may not make sense right away but trust me and do it anyway. It will make sense in a few exercises.

Most of what software does is the following:

1. Take some kind of input from a person.
2. Change it.
3. Print out something to show how it changed.

So far you have been printing strings, but you haven't been able to get any input from a person. You may not even know what "input" means, but type this code in anyway and make it exactly the same. In the next exercise we'll do more to explain input.

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print "How old are you?", age = raw_input() print "How tall are you?", height = raw_input() print "How much do you weigh?", weight = raw_input() print "So, you're %r old, %r tall and %r heavy." % ( age, height, weight) What You Should See $ python ex11.py How old are you? 38 How tall are you? 6'2" How much do you weigh? 180lbs So, you're '38' old, '6\'2"' tall and '180lbs' heavy. print ("How old are you?"), age = input() print ("How tall are you?"), height = input() print ("How much do you weigh?"), weight = input() print ("So, you're %r old, %r tall and %r heavy." % ( age, height, weight)) >>> ================= RESTART =================== >>> How old are you? 12 How tall are you? 176 How much do you weigh? 67 So, you're '12' old, '176' tall and '67' heavy. >>>

Exercise 10: What Was That?

Exercise 10: What Was That?

In Exercise 9 I threw you some new stuff, just to keep you on your toes. I showed you two ways to make a string that goes across multiple lines. In the first way, I put the characters \n (backslash n) between the names of the months. These two characters put a new line character into the string at that point.

This \ (backslash) character encodes difficult-to-type characters into a string. There are various "escape sequences" available for different characters you might want to use. We'll try a few of these sequences so you can see what I mean.

An important escape sequence is to escape a single-quote ' or double-quote ". Imagine you have a string that uses double-quotes and you want to put a double-quote inside the string. If you write "I "understand" joe." then Python will get confused because it will think the " around "understand" actually ends the string. You need a way to tell Python that the " inside the string isn't a real double-quote.

To solve this problem you escape double-quotes and single-quotes so Python knows to include in the string. Here's an example:

"I am 6'2\" tall."  # escape double-quote inside string
'I am 6\'2" tall.'  # escape single-quote inside string

The second way is by using triple-quotes, which is just """ and works like a string, but you also can put as many lines of text as you want until you type """ again. We'll also play with these.

tabby_cat = "\tI'm tabbed in."

persian_cat = "I'm split\non a line."

backslash_cat = "I'm \\ a \\ cat."

fat_cat = """

I'll do a list:

\t* Cat food

\t* Fishies

\t* Catnip\n\t* Grass

"""

print (tabby_cat)

print (persian_cat)

print (backslash_cat)

print (fat_cat)

>>> ============ RESTART =============

>>> 

I'm tabbed in.

I'm split

on a line.

I'm \ a \ cat.

I'll do a list:

* Cat food

* Fishies

* Catnip

* Grass

>>> 

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tabby_cat = "\tI'm tabbed in." persian_cat = "I'm split\non a line." backslash_cat = "I'm \\ a \\ cat." fat_cat = """ I'll do a list: \t* Cat food \t* Fishies \t* Catnip\n\t* Grass """ print tabby_cat print persian_cat print backslash_cat print fat_cat

What You Should See

Look for the tab characters that you made. In this exercise the spacing is important to get right.

$ python ex10.py
        I'm tabbed in.
I'm split
on a line.
I'm \ a \ cat.

I'll do a list:
        * Cat food
        * Fishies
        * Catnip
        * Grass

Escape Sequences

This all of the escape sequences Python supports. You may not use many of these, but memorize their format and what they do anyway. Try them out in some strings to see if you can make them work.

ESCAPE	WHAT IT DOES.
\\	Backslash ()
\'	Single-quote (')
\"	Double-quote (")
\a	ASCII bell (BEL)
\b	ASCII backspace (BS)
\f	ASCII formfeed (FF)
\n	ASCII linefeed (LF)
\N{name}	Character named name in the Unicode database (Unicode only)
\r ASCII	Carriage Return (CR)
\t ASCII	Horizontal Tab (TAB)
\uxxxx	Character with 16-bit hex value xxxx (Unicode only)
\Uxxxxxxxx	Character with 32-bit hex value xxxxxxxx (Unicode only)
\v	ASCII vertical tab (VT)
\ooo	Character with octal value ooo
\xhh	Character with hex value hh

Here's a tiny piece of fun code to try out:

while True:
    for i in ["/","-","|","\\","|"]:
        print "%s\r" % i,

Exercise 9: Printing, Printing, Printing

By now you should realize the pattern for this book is to use more than one exercise to teach you something new. I start with code that you might not understand, then more exercises explain the concept. If you don't understand something now, you will later as you complete more exercises. Write down what you don't understand, and keep going.

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# Here's some new strange stuff, remember type it exactly. days = "Mon Tue Wed Thu Fri Sat Sun" months = "Jan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug" print "Here are the days: ", days print "Here are the months: ", months print """ There's something going on here. With the three double-quotes. We'll be able to type as much as we like. Even 4 lines if we want, or 5, or 6. """

What You Should See

$ python ex9.py
Here are the days:  Mon Tue Wed Thu Fri Sat Sun
Here are the months:  Jan
Feb
Mar
Apr
May
Jun
Jul
Aug

There's something going on here.
With the three double-quotes.
We'll be able to type as much as we like.
Even 4 lines if we want, or 5, or 6.

# Here's some new strange stuff, remember type it exactly.

days = "Mon Tue Wed Thu Fri Sat Sun"
months = "Jan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug"

print ("Here are the days: ", days)
print ("Here are the months: ", months)

print ("""
There's something going on here.
With the three double-quotes.
We'll be able to type as much as we like.
Even 4 lines if we want, or 5, or 6.
""")

>>> ======== RESTART =======================
>>> 
Here are the days:  Mon Tue Wed Thu Fri Sat Sun
Here are the months:  Jan
Feb
Mar
Apr
May
Jun
Jul
Aug

There's something going on here.
With the three double-quotes.
We'll be able to type as much as we like.
Even 4 lines if we want, or 5, or 6.

>>> 

Exercise 8: Printing, Printing

We will now see how to do a more complicated formatting of a string. This code looks complex, but if you do your comments above each line and break each thing down to its parts, you'll understand it.

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formatter = "%r %r %r %r" print formatter % (1, 2, 3, 4) print formatter % ("one", "two", "three", "four") print formatter % (True, False, False, True) print formatter % (formatter, formatter, formatter, formatter) print formatter % ( "I had this thing.", "That you could type up right.", "But it didn't sing.", "So I said goodnight." )

What You Should See

$ python ex8.py
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'one' 'two' 'three' 'four'
True False False True
'%r %r %r %r' '%r %r %r %r' '%r %r %r %r' '%r %r %r %r'
'I had this thing.' 'That you could type up right.' "But it didn't sing." 'So I said goodnight.'

Study this carefully and try to see how I put the formatter inside the formatter.

formatter = "%r %r %r %r"

print (formatter % (1, 2, 3, 4))
print (formatter % ("one", "two", "three", "four"))
print (formatter % (True, False, False, True))
print (formatter % (formatter, formatter, formatter, formatter))
print (formatter % (
    "I had this thing.",
    "That you could type up right.",
    "But it didn't sing.",
    "So I said goodnight."
))

>>> ============= RESTART ============
>>> 
1 2 3 4
'one' 'two' 'three' 'four'
True False False True
'%r %r %r %r' '%r %r %r %r' '%r %r %r %r' '%r %r %r %r'
'I had this thing.' 'That you could type up right.' "But it didn't sing." 'So I said goodnight.'
>>> 

Exercise 7: More Printing

Exercise 7: More Printing

print ("Mary had a little lamb.")
print ("Its fleece was white as %s." % 'snow')
print ("And everywhere that Mary went.")
print ("." * 10 ) # what'd that do?

end1 = "C"
end2 = "h"
end3 = "e"
end4 = "e"
end5 = "s"
end6 = "e"
end7 = "B"
end8 = "u"
end9 = "r"
end10 = "g"
end11 = "e"
end12 = "r"

# watch that comma at the end.  try removing it to see what happens
print (end1 + end2 + end3 + end4 + end5 + end6,)
print (end7 + end8 + end9 + end10 + end11 + end12)

>>> ================ RESTART =====================
>>>
Mary had a little lamb.
Its fleece was white as snow.
And everywhere that Mary went.
..........
Cheese
Burger
>>>

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print "Mary had a little lamb." print "Its fleece was white as %s." % 'snow' print "And everywhere that Mary went." print "." * 10 # what'd that do? end1 = "C" end2 = "h" end3 = "e" end4 = "e" end5 = "s" end6 = "e" end7 = "B" end8 = "u" end9 = "r" end10 = "g" end11 = "e" end12 = "r" # watch that comma at the end. try removing it to see what happens print end1 + end2 + end3 + end4 + end5 + end6, print end7 + end8 + end9 + end10 + end11 + end12

What You Should See

$ python ex7.py
Mary had a little lamb.
Its fleece was white as snow.
And everywhere that Mary went.
..........
Cheese Burger

Exercise 5: More Variables and Printing

Now we'll do even more typing of variables and printing them out. This time we'll use something called a "format string." Every time you put " (double-quotes) around a piece of text you have been making a string. A string is how you make something that your program might give to a human. You print strings, save strings to files, send strings to web servers, and many other things.

my_name = 'Zed A. Shaw'

my_age = 35 # not a lie

my_height = 74 # inches

my_weight = 180 # lbs

my_eyes = 'Blue'

my_teeth = 'White'

my_hair = 'Brown'

print ("Let's talk about %s." % my_name)

print ("He's %d inches tall." % my_height)

print ("He's %d pounds heavy." % my_weight)

print ("Actually that's not too heavy.")

print ("He's got %s eyes and %s hair." % (my_eyes, my_hair))

print ("His teeth are usually %s depending on the coffee." % my_teeth)

# this line is tricky, try to get it exactly right

print ("If I add %d, %d, and %d I get %d." % (

    my_age, my_height, my_weight, my_age + my_height + my_weight))

>>> ================= RESTART ================

>>> 

Let's talk about Zed A. Shaw.

He's 74 inches tall.

He's 180 pounds heavy.

Actually that's not too heavy.

He's got Blue eyes and Brown hair.

His teeth are usually White depending on the coffee.

If I add 35, 74, and 180 I get 289.

>>> 

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my_name = 'Zed A. Shaw' my_age = 35 # not a lie my_height = 74 # inches my_weight = 180 # lbs my_eyes = 'Blue' my_teeth = 'White' my_hair = 'Brown' print "Let's talk about %s." % my_name print "He's %d inches tall." % my_height print "He's %d pounds heavy." % my_weight print "Actually that's not too heavy." print "He's got %s eyes and %s hair." % (my_eyes, my_hair) print "His teeth are usually %s depending on the coffee." % my_teeth # this line is tricky, try to get it exactly right print "If I add %d, %d, and %d I get %d." % ( my_age, my_height, my_weight, my_age + my_height + my_weight) What You Should See $ python ex5.py Let's talk about Zed A. Shaw. He's 74 inches tall. He's 180 pounds heavy. Actually that's not too heavy. He's got Blue eyes and Brown hair. His teeth are usually White depending on the coffee. If I add 35, 74, and 180 I get 289.

Exercise 6: Strings and Text

While you have been writing strings, you still do not know what they do. In this exercise we create a bunch of variables with complex strings so you can see what they are for. First an explanation of strings.

x = "There are %d types of people." % 10

binary = "binary"

do_not = "don't"

y = "Those who know %s and those who %s." % (binary, do_not)

print (x)

print (y)

print ("I said: %r." % x)

print ("I also said: '%s'." % y)

hilarious = False

joke_evaluation = "Isn't that joke so funny?! %r"

print (joke_evaluation % hilarious)

w = "This is the left side of..."

e = "a string with a right side."

print (w + e)

>>> =============== RESTART =================

>>> 

There are 10 types of people.

Those who know binary and those who don't.

I said: 'There are 10 types of people.'.

I also said: 'Those who know binary and those who don't.'.

Isn't that joke so funny?! False

This is the left side of...a string with a right side.

>>> 

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x = "There are %d types of people." % 10 binary = "binary" do_not = "don't" y = "Those who know %s and those who %s." % (binary, do_not) print x print y print "I said: %r." % x print "I also said: '%s'." % y hilarious = False joke_evaluation = "Isn't that joke so funny?! %r" print joke_evaluation % hilarious w = "This is the left side of..." e = "a string with a right side." print w + e

What You Should See

$ python ex6.py
There are 10 types of people.
Those who know binary and those who don't.
I said: 'There are 10 types of people.'.
I also said: 'Those who know binary and those who don't.'.
Isn't that joke so funny?! False
This is the left side of...a string with a right side.