this week the string type modules print statement writing programs if statements (time permitting)...

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