Week 3: Tuesday

I-P-0

Input Process Output

Accepting numerics (type casting)

• input() always returns a string
• To accept a number, convert it to the desired type
• int() converts to integer
• float() converts to floating point

Example

age = input("Enter your age: ")
age = int(age)

# or

age = int(input("Enter your age: "))

---

Input Validation	Definition
str.isalpha()	True if all alphabetic
str.isdigit()	True if all digits
str.isalnum()	True if all alphanumeric
str.isdecimal()	True if all 0-9
str.isnumeric()	True if all numeric
str.islower()	True if all lowercase
str.isupper()	True if all uppercase

Example

# imagine these are inputs, This won't let me do an input
name = "something"
age = "20"


if name.isalpha():
    print("name is alpha")
else:
    print("name is not alpha")

if age.isdigit():
    print("age is digit")
else:
    print("age is not digit")

if age.isdecimal():
    print("age is decimal")
else:
    print("age is not decimal")

name is alpha
age is digit
age is decimal

Try Except validation, the best kind

• Since we are talking about validation, we can also use try and except to catch errors.
• try except tries to do something and something else if it fails.
• It handles errors gracefully without breaking everything.
• Different Errors: ValueError, TypeError, IndexError.
• See documentation for more errors.

Try Except, Example 1 (Good)

try:
    age = "12.0"
    print(age.isnumeric())
    if not age.isnumeric():
        raise ValueError("Age is not numeric")
    print("Age is", age)
except ValueError as e:
    print(e)

False
Age is not numeric

Try Except, Example 2 (bad)

try:
    age = "120"
    if not age.isnumeric():
        raise ValueError("Age is not numeric")
except ValueError as e:
    print(e)

print("Age is ", age)

Age is  120

Try Except, Example 3

try:
    upper = "HELLo"
    if not upper.isupper():
        raise ValueError("Not all uppercase")
    print(f"{upper} is all uppercase")
except Exception as e:
    print(e)

Not all uppercase

Processing

• Doing stuff to the stuff
• it’s the verb in the IPO: input, process, output
• input = information, process = action, output = result
• Could be simple:
  • Adding, concatinating, subtracting, multiplying, dividing, averaging, etc.
• or complex:
  • Data Cleaning, Data wrangling, transforming, modeling, etc.

Processing Example

information = [i for i in range(1, 33, 3)]  # input
avg = sum(information) / len(information)  # process
print(f"information = {information}")  # output
print(f"Average of information is {avg}")  # output

information = [1, 4, 7, 10, 13, 16, 19, 22, 25, 28, 31]
Average of information is 16.0

f strings

• f strings are a way to format strings
• f"string {variable} string"

name = "John"
age = 20
print(f"Hello, my name is {name} and I am {age} years old.")

Hello, my name is John and I am 20 years old.

String Functions

---

String Method	Explanation
str.capitalize()	“homer” → “Homer”
str.upper()	“homer” → “HOMER”
str.lower()	“HOMER” → “homer”
str.title()	“homer simpson” → “Homer Simpson”
str.swapcase()	“Homer Simpson” → “hOMER sIMPSON”
str.strip()	” homer ” → “homer”

Example

name = "    homer SIMPSON    "
nameb = "homer simpson"
print("capitalize", name.capitalize())  # capitalizes first character
print("capitalize", nameb.capitalize())
print("upper", name.upper())
print("lower", name.lower())
print("title", name.title())
print("swapcase", name.swapcase())
print("strip", name.strip())

capitalize     homer simpson    
capitalize Homer simpson
upper     HOMER SIMPSON    
lower     homer simpson    
title     Homer Simpson    
swapcase     HOMER simpson    
strip homer SIMPSON

---

String Functions	Explanation
len(string)	“something” → 9
string.count(“s”)	“something” → 1
min(string)	“something” → “e”
max(string)	“something” → “t”
“s” in “something”	True if “s” in “something”
“s” not in “something”	True if “s” not in “something”
“some” * 3	“some” → “somesomesome”

---

String Functions	Explanation
“some”[3]	“some” → “e”
“some”[1:3]	“some” → “om”
“some”[0:3:2]	“some” → “se”

Example

first_name = "Nathan"
last_name = "Michalewicz"
print("Length of first name is", len(first_name))
print("Count of 'a' in first name is", first_name.count("a"))
print("Min of first name is", min(first_name))
print("Max of first name is", max(first_name))
print("Is 'a' in first name?", "a" in first_name)
print("Is 'a' not in first name?", "a" not in first_name)
print("first name * 3 is", first_name * 3)
print("first name[3] is", first_name[3])
print("first name[1:3] is", first_name[1:3])
print("first name[0:3:2] is", first_name[0:3:2])

Length of first name is 6
Count of 'a' in first name is 2
Min of first name is N
Max of first name is t
Is 'a' in first name? True
Is 'a' not in first name? False
first name * 3 is NathanNathanNathan
first name[3] is h
first name[1:3] is at
first name[0:3:2] is Nt

---

More String Function	Explanation
string.join(iterable)	” “.join([”a”, ”b”, ”c”]) →”a b c”
string.partition("o")	“something” → (“s”, “o”, “mething”) (returns a 3-tuple)
string.rpartition("o")	“something” → (“so”, “m”, “ing”) (returns a 3-tuple)
string.split(" ")	“a b c” → [“a”, “b”, “c”] (returns a list)

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More String Function	Explanation
string.split(sep, max)	returns list splitting until max intervals
string.rsplit(sep, max)	returns list splitting until max intervals backwards
string.splitlines()	returns list split at lines

Example

lname = "Michalewicz"
fname = "Nathan"
s = "a b c d e f g"
lines = "a\nb\nc\nd\ne\nf\ng"  # \n is a newline character
print(fname.partition("a"))
print(fname.rpartition("a"))
print(s.split(" ", 3))
print(s.rsplit(" ", 3))
print(lines.splitlines())

('N', 'a', 'than')
('Nath', 'a', 'n')
['a', 'b', 'c', 'd e f g']
['a b c d', 'e', 'f', 'g']
['a', 'b', 'c', 'd', 'e', 'f', 'g']

---

Spacing Functions	Explanation
string.ljust(10)	“a” → “a”
string.rjust(10)	“a” → ” a”
string.center(10)	“a” → ” a ”
string.zfill(10)	“a” → “000000000a”
string.center(10, "-")	“a” → “—-a—–”

---

Spacing Functions	Explanation
string.expandtabs(10)	“a b” → “a b”
string.strip()	” a ” → “a”
string.lstrip()	” a ” → “a”
string.rstrip()	” a ” → ” a”

Example

s = "a"
print("ljust", s.ljust(10))
print("rjust", s.rjust(10))
print("center", s.center(10))
print("zfill", s.zfill(10))
print("center", s.center(10, "-"))
print("expandtabs", "a\tb".expandtabs(10))
print(".strip", "  a  ".strip())
print(".lstrip", "  a  ".lstrip())
print(".rstrip", "  a  ".rstrip())

ljust a         
rjust          a
center     a     
zfill 000000000a
center ----a-----
expandtabs a         b
.strip a
.lstrip a  
.rstrip   a

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Find/Replace Functions	Examples
string.find("s")	returns lowest index of s
string.rfind("s")	returns highest occurrence of s
string.index("s")	returns first occurrence of s
string.rindex("s")	returns highest index of s
string.replace("s", "t")	replaces s with t
string.replace("s", "t", 3)	replaces s with t a max of 3 times.

Example

s = "Nathan"
print("find: ", s.find("a"))
print("rfind: ", s.rfind("a"))
print("index: ", s.index("a"))
print("rindex: ", s.rindex("a"))
print("replace: ", s.replace("a", "o"))
print("replace: ", s.replace("a", "o", 1))

find:  1
rfind:  4
index:  1
rindex:  4
replace:  Nothon
replace:  Nothan

Number Functions

---

Basic Functions	Explanation
abs(x)	absolute value of x
max(x, y, z)	maximum of x, y, z
min(x, y, z)	minimum of x, y, z
pow(x, y)	x to the power of y
round(x [,n])	rounds x to the nearest integer and rounds to n decimals

Example

number = -4.12312
l = [1, 2, 3, 4, 5]
t = (1, 2, 3, 4, 5)
print("abs: ", abs(number))
print("max: ", max(l))
print("max: ", max(t))
print("min: ", min(l))
print("pow: ", pow(number, 3))
print("round: ", round(number, 2))

abs:  4.12312
max:  5
max:  5
min:  1
pow:  -70.09352873155534
round:  -4.12

---

Advanced Functions	Explanation
math.copysign(x, y)	returns x with the sign of y
math.fabs(x)	absolute value of x
math.factorial(x)	factorial () of x
math.floor(x)	returns the floor of x
math.ceil(x)	returns the ceiling of x
math.fmod(x, y)	returns the remainder of x/y

Example

import math  # IMPORTANT!!!! import math

x = -4
y = 3
z = 4.712

print("copysign: ", math.copysign(x, y))
print("fabs: ", math.fabs(x))
print("factorial: ", math.factorial(5))
print("floor: ", math.floor(z))
print("ceil: ", math.ceil(z))

copysign:  4.0
fabs:  4.0
factorial:  120
floor:  4
ceil:  5

---

• We will not go over the math module in greater detail. We have classes for that.
• See the book for more detail.

---

random functions	Explanation
random.choice(iter)	random choice from iterable
random.randint(x, y)	random integer between x and y
random.random()	random float between 0 and 1
random.randrange(x, y, z)	random integer between x and y with step z
random.shuffle(iter)	shuffles iterable in place
random.seed(x)	sets the seed for random

Example

import random  # IMPORTANT!!!! import random

l = [1, 2, 3, 4, 5]
r = []
print("choice: ", random.choice(l))
print("randint: ", random.randint(1, 10))
print("random: ", random.random())
print("randrange: ", random.randrange(1, 10, 2))
random.shuffle(l)
print("shuffle: ", l)
print("seed: ", r)

choice:  1
randint:  7
random:  0.4788783949238976
randrange:  1
shuffle:  [4, 3, 2, 5, 1]
seed:  []

Random Seed

• Random seed is a way to set the random number generator to a specific number, so it is reproducable

random.seed(4)
print(random.randint(1, 100))
print(random.randint(1, 100))

31
39

random.seed(4)
print(random.randint(1, 100))
print(random.randint(1, 100))

31
39

Datetime

• datetime is a module that allows you to work with dates and times
• datetime.datetime.now() returns the current date and time
• datetime.datetime(year, month, day) returns a date object
• datetime.datetime.strptime(date, format) returns a date object from a string
• typical format is "%Y-%m-%d %H:%M:%S"
• can also use strftime to format a date object

Why we need date objects

from datetime import datetime  # IMPORTANT!!!! import datetime

nathan = "1986-02-14"
rebecca = "1985-04-16"

# print(datetime.now())

if nathan > rebecca:
    print("nathan came later")
else:
    print("rebecca is older")

nathan came later

• But rebecca is older.

Why we need date objects, 2

• strptime() : string parse time
• strftime() : string format time

n = datetime.strptime(nathan, "%Y-%m-%d")
r = datetime.strptime(rebecca, "%Y-%m-%d")

if datetime.now() - n > datetime.now() - r:
    print(f"nathan is older, he was born {datetime.strftime(n, '%B %d, %Y')}")
else:
    print(f"rebecca is older, she was born {datetime.strftime(r, '%B %d, %Y')}")

print(f"In case you were wondering that was a {r.weekday()}")

rebecca is older, she was born April 16, 1985
In case you were wondering that was a 1

Weekdays return 0-6

• Monday is 0
• Sunday is 6

days = {
    0: "Monday",
    1: "Tuesday",
    2: "Wednesday",
    3: "Thursday",
    4: "Friday",
    5: "Saturday",
    6: "Sunday",
}

print(f"Rebecca was born on a {days[r.weekday()]} in {r.year}")

Rebecca was born on a Tuesday in 1985

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str format	Explanation
%a	Weekday, short version
%A	Weekday, full version
%w	Weekday as a number 0-6
%d	Day of month 01-31
%b	Month name, short version
%B	Month name, full version
%m	Month as a number 01-12
%y	Year, short version, without century
%Y	Year, full version

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str format	Explanation
%H	Hour 00-23
%I	Hour 00-12
%p	AM/PM
%M	Minute 00-59
%S	Second 00-59
%f	Microsecond 000000-999999
%z	UTC offset
%Z	Timezone

Example

print(datetime.strftime(r, "%A, %B %d, %Y"))
print(datetime.strftime(n, "%I:%M:%S %p"))
print(datetime.strftime(n, "%a, %Y, %B %d"))

Tuesday, April 16, 1985
12:00:00 AM
Fri, 1986, February 14

Time delta

• timedelta is a way to add or subtract time from a date object

from datetime import timedelta, datetime

if datetime.now() - (r + timedelta(days=365)) < datetime.now() - n:
    print(f"Only in this python world is Rebecca younger")
else:
    print("Rebecca is older")

Only in this python world is Rebecca younger