This Week

The string type

Modules

print statement

Writing programs

if statements (time permitting)

The boolean type (time permitting)

Review of Functions

defIs a keyword

parameters zero or more, comma-separated

bodyOne or more statementsA return statement only exists in a function body

Exampledef square(x): return x**2

def function_name(parameters):

body

The Type StringSingle ‘…’ and double “…” quotes:

‘This is a string’ and “this is a string.”

Triple ```…’’’ quote:```This is a really long string that spans more than one line.’’’

Concatenation “Good ” + “Morning” “Good Morning”

The print Statement

When we want to output information to the screen we use print().

>>>print(“hello”)hello

>>>print(“5+6=”, 5+6)5+6=11

4

Writing Programs

A file is a program when we makefunction calls inside the file.

Q. How?

Put the function call inside a “main clause” at the end of the file:

if __name__ == '__main__':

cube_volume(5)

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 import

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

– Prevents ambiguity

– But inconvenient to type math.pow

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 pow(2,3)

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

Documentation Strings

Documentation Strings (docstrings)

• Use to explain the code

• Must be a string and the first line in a

function or module

• Use complete, grammatically correct

sentences

• Use parameter names, mention their types

and describe the return value and type

The “if” StatementEnglish example:

Check The Temperature:If the temperature > 0 then

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”

The “if” StatementPython example:

def check_temp(temperature):If the temperature > 0 then

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”

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 thenit 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 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”

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

Boolean

These objects are either true or false.

In Python, the type is bool.

Examples>>> 3>5

>>> False

>>> 2<10

>>> True

Combining Booleans: and, or, nottrue and true

3<4 and 3>2?

True

true and false3<4 and 2>5?

False

false and false6<2 and 2>5?

False

true or false6<10 or 2>5?

True

not truenot 1<4

False

not falsenot 6<2

True

Relational Operators

<, >, <=, >=, ==, !=

Precedence: How does Python evaluate25 < 12 + 35 ?

25 < 47 ?True

Order: arithmetic relational boolean