Last WeekModules• Save functions to a file, e.g., filename.py• The file filename.py is a module• We can use the functions in filename.py

by importing it

Docstrings• Use to explain the code• Must be a string and the first line in a

function or module• Include parameter names, mention their

types and describe the return value and type

This Week

More on modules

New Python statementsif statementprint statement details

input builtin functionfor … in …: statement

The boolean type

Modules

• Sometimes we want to use some functions frequently

• Save them to a file, e.g., filename.py

• Include them with the Python command import filename

• We call this file a module.

Modules

• Python has builtin functions, e.g., – pow(x,y) returns xy

– sqrt(x) returns √x

• Organized into different modules (stored in different files)

• pow(x,y) and sqrt(x) belong to the math module

More on importimport math

– Need to say math.sqrt(2,3) to use sqrt()

– Prevents ambiguity

– But inconvenient to type math.sqrt

Solution– Only import specific functions:

>>> from math import pow, sqrt – Import all functions when you know there

are no conflicts>>> from math import *

– Now we can say sqrt(5)

The __builtins__ Module

•Ways to get help with functions:

– dir(module): list the functions in a module

– help(function): show the docstrings for a function or module

– import module: include the functions defined in a module

The “if” StatementEnglish example:

Check The Temperature:

If the temperature > 0 then it is “above the freezing point”

Otherwise, if the temperature = 0 thenit is “at the freezing point”

Otherwise it is “below the freezing point”

The “if” StatementPython example:

def check_temp(temperature):

If the temperature > 0 then it is “above the freezing point”

Otherwise, if the temperature = 0 thenit is “at the freezing point”

Otherwise it is “below the freezing point”

The “if” StatementPython example:

def check_temp(temperature):if temperature > 0:

return “above the freezing point”

Otherwise, if the temperature = 0 thenit is “at the freezing point”

Otherwise it is “below the freezing point”

The “if” StatementPython example:

def check_temp(temperature):

if temperature > 0:

return “above the freezing point”

elif temperature == 0:

return “at the freezing point”

Otherwise it is “below the freezing point”

The “if” StatementPython example:

def check_temp(temperature):

if temperature > 0:

return “above the freezing point”

elif temperature == 0:

return “at the freezing point”else:

return “below the freezing point”

The “if” Statement

English Python

If condition if condition:

Otherwise, if condition elif condition:

Otherwise else:

Nested “if” StatementsEnglish example:

Check The Temperature:

If the temperature > 0 then if the temperature >100 then

it is “above the boiling point”Otherwise, if the temperature> 37 then

it is “above body temperature”Otherwise,

it is “above the freezing point”Otherwise, if the temperature = 0 then

it is “at the freezing point”Otherwise

it is “below the freezing point”

Nested “if” StatementsEnglish example:

def check_temp(temperature):

if temperature > 0:

if the temperature >100 thenit is “above the boiling point”

Otherwise, if the temperature> 37 thenit is “above body temperature”

Otherwise, it is “above the freezing point”

elif temperature == 0:

return “at the freezing point”else:

return “below the freezing point”

Nested “if” StatementsEnglish example:

def check_temp(temperature):

if temperature > 0:

if temperature > 100:

return “above the boiling point”Otherwise, if the temperature > 37 then

it is “above body temperature”Otherwise,

it is “above the freezing point”elif temperature == 0:

return “at the freezing point”else:

return “below the freezing point”

Nested “if” StatementsEnglish example:

def check_temp(temperature):

if temperature > 0:

if temperature > 100:

return “above the boiling point”elif temperature > 37:

return “above body temperature”Otherwise,

it is “above the freezing point”elif temperature == 0:

return “at the freezing point”else:

return “below the freezing point”

English example:

def check_temp(temperature):

if temperature > 0:

if temperature > 100:

return “above the boiling point”elif temperature > 37:

return “above body temperature”else:

return “above the freezing point”elif temperature == 0:

return “at the freezing point”else:

return “below the freezing point”

Nested “if” Statements

>100

>37 and <=100

>0 and <=37

Getting User Input

When we want to display information to the screen we use print.

>>> print(“hello”)>>> print(5+6)

When we want get input from the user we use the builtin function input.

>>> input()>>> name = input(“Enter name:”)

Getting User Input

Q. What does input return?

A. input() always returns a string.

Suppose we need an integer value from the user.

>>> age = input(“Enter your age:”)

Q. How can we convert input’s return value to be an integer?A.

>>> age = int(input(“Enter your age:”))

More on StringsQ. What is a string exactly?

A. A sequence of characters with position numbers called indices.

“Hello World”: “H” is at index 0.

Q. How can we select parts of a string?

A. We can select a particular character by specifying its index:

>>>”Hello World”[2]“l”

More on Strings We can select part of a string by specifying a range.

>>>”Hello Class”[1:6]“ello ”

Q. What string would “Hello Class”[3:] return?A. >>>”Hello Class”[3:]

“lo Class”

Q. What string would “Hello Class”[:2] return?A. >>>”Hello Class”[:2]

“He”

More on Strings

Q. What else can we do to strings?

A. There are many methods that apply to strings:• “Hello World”.replace(“World”,“Class”)• “Hello Class”.count(“l”)• “Hello Class”.find(“as”)

The functions replace, count and find are called methods because they behave like operators.

Q. How would you find all the methods for strings?

A. dir(str)

String Methods

s.isupper():

returns True if s is all upper case, False otherwise.

s.islower():

returns True if s is all lower case, False otherwise.

s.isdigit():

returns True if s is a number, False otherwise.

s.upper():

returns a copy of s in all upper case.

s.lower():

returns a copy of s in all lower case.

String Methods

len(s): returns the length of s.

sub in s: returns true if sub is a substring of s.

We know what “anna” + “anna” returns.

Q. What about “anna”*4 ?

“annaannaannaanna”

Visiting the Items in a String S

Printing out the characters of the string

English:for each char in S

print the charPython:

for char in S:

print(char)

Notes:char is a variable namefor and in are Python key words

for loopsFormat:

for variable in string:

statements

Example with strings:

name = ”Edward”

new = “”

for letter in name:

new = letter + new

print(new)

Strings Using Conversion SpecifiersWe sometimes would like to insert values of variables into strings:A1 = 60A2 = 75A3 = 88

We would like: ‘The average of 60, 75 and 88 is 74.33.’

How do we print this with our variables?

>>>print(‘The average of’, A1, ‘,’, A2, ‘ and ’, A3, ‘ is ’, (A1+A2+A3)/3)

Does this work?

Strings Using Conversion SpecifiersWe displayed:‘The average of 60 , 75 and 88 is 74.33333333333333 .’

Q. What’s wrong?A. Spacing is wrong around commas and periods.

We have many more decimal places than wanted.

Q. How can we fix it?A. Use conversion specifiers.

>>>print(‘The average of %d, %d and %d is %.2f’ %(A1, A2, A3, (A1+A2+A3)/3.0))

The average of 60, 75 and 88 is 74.33.

Common Conversion Specifiers

%d display the object as a decimal integer

%f display the object as a floating point with 6 decimal places%.2f display the object as a floating point with 2 decimal places%s display the object as a string

Q. What else do we use % for?

A. Modulus. We say that % is overloaded.