Walkthrough:
Conditionals Program

Let’s walk through writing a program that helps make decisions when picking out what to pack for a day trip.

We’ll start with the following high-level description of our approach, then refine down to pseudocode that is close to what we could implement in Python.

Descriptive level. Write in full prose:

Determine the place you're going (beach, mountain, or park). Get something

to carry your supplies (tote for the beach, backpack for the mountain, picnic

basket for the park). Check the weather to pack appropriately. If it's sunny,

pack sunglasses. If it's sunny and you're going to the beach or the park, pack

sunblock. If it's raining, grab an umbrella. If you're going to the beach, pack

a towel. If you're going to the mountain, pack a flashlight.

Refinement 1. Use line breaks to separate different actions:

Determine the place you're going (beach, mountain, or park).

Get something to carry your supplies

(tote for the beach, backpack for the mountain, picnic basket for the park).

Check the weather and

pack appropriately.

If it's sunny, pack sunglasses.

If it's sunny and you're going to the beach or the park, pack sunblock.

If it's raining, grab an umbrella.

If you're going to the beach, pack a towel.

If you're going to the mountain, pack a flashlight.

Refinement 2. Reorder and reword to make actions sequential:

Determine the place you're going (beach, mountain, or park).

Get something to carry your supplies

(tote for the beach, backpack for the mountain, picnic basket for the park).

Check the weather

pack appropriately.

If it's sunny, pack sunglasses.

If it's sunny and you're going to the beach or the park, pack sunblock.

If it's raining, grab an umbrella.

If you're going to the beach, pack a towel.

If you're going to the mountain, pack a flashlight.

Refinement 3. Make actions simpler and more concise by removing irrelevant phrases:

Determine place (beach, mountain, or park).

Get supply-carrier

(tote for beach, backpack for mountain, picnic basket for park).

Check weather and

pack appropriately.

If sunny, sunglasses.

If sunny and (beach or park), sunblock.

If raining, umbrella.

If beach, towel.

If mountain, flashlight.

Refinement 4. Separate conjunctive phrases to make each line contain exactly one action/instruction:

Determine place (beach, mountain, or park).

Get supply-carrier

(tote for beach, backpack for mountain, picnic basket for park).

Check weather

pack appropriately.

If sunny, sunglasses.

If sunny and (beach or park), sunblock.

If raining, umbrella.

If beach, towel.

If mountain, flashlight.

Refinement 5. Identify conditional and use keyword if; add colons (:) to identify actions (e.g., verbs) and any required objects:

Determine place (beach, mountain, or park)

Get supply-carrier for place

IF beach

get: tote

ELSE IF mountain

get: backpack

ELSE IF park

get: picnic basket

Check weather

Pack for weather, place

IF sunny

pack: sunglasses

IF sunny and (beach or park)

pack: sunblock

IF raining

pack: umbrella

IF beach

pack: towel

IF mountain

pack: flashlight

1. Turn each line of pseudocode into a comment

2. Translate each line into Python

def getSupplyCarrier( place ):

""" Given a place ("beach", "mountain" or "park"),

get the right supply carrier"""

# IF beach

if place == "beach":

# get: tote

return "tote"

# ELSE IF mountain

elif place == "mountain":

# get: backpack

return "backpack"

# ELSE IF park

elif place == "park":

# get: picnic basket

return "picnic basket"

# placeholder return

return "TBD carrier"

def packFor( weather, place ):

""" Given the weather ("sunny" or "raining")

and a place ("beach", "mountain" or "park"),

pack the right supplies!"""

supplyList = "" # start with no supplies

# IF sunny

if weather == "sunny":

# pack: sunglasses

supplyList = supplyList + "sunglasses, "

# IF sunny and (beach or park)

if weather == "sunny" and ((place == "beach") or (place == "park")):

# pack: sunblock

supplyList = supplyList + "sunblock, "

# IF raining

if weather == "raining":

# pack: umbrella

supplyList = supplyList + "umbrella, "

# IF beach

if place == "beach":

# pack: towel

supplyList = supplyList + "towel, "

# IF mountain

if place == "mountain":

# pack: flashlight

supplyList = supplyList + "flashlight, "

# take off extra ", "

supplyList = supplyList[0:len(supplyList)-2]

return supplyList

# Determine: place (beach, mountain, or park)

place = input( "Where are you going today? [beach/mountain/park]: ")

# Get: supply carrier

carrier = getSupplyCarrier( place )

# Check: weather

weather = input( "What is the weather like? [sunny/raining]: ")

# Pack for: weather, place

packItems = packFor( weather, place )

print( "Get a " + carrier + " and put your " + packItems + " inside. Enjoy your trip!" )