Python 101

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

Let's create a file called birthday.py


BIRTHDAY = "1982-09-08"
print(BIRTHDAY)

Always run your script after each exercise!

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

Change birthday.py to look like this:


BIRTHDAY = "1982-09-08"
message = "I am born on {}".format(BIRTHDAY)
print(message)

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

With this new knowledge we can extend birthday.py a bit...
Let's make it so that we pass in the date via the command line
Make it look like this:


import sys

BIRTHDAY = sys.argv[1]
message = "I am born on {}".format(BIRTHDAY)
print(message)

Try to press the "Run" button

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

Let's build some error handling into our birthday.py


import sys

if len(sys.argv) < 2:
    print("ERROR: Please provide a date")
else:
    BIRTHDAY = sys.argv[1]
    message = "I am born on {}".format(BIRTHDAY)
    print(message)

By the way: "len" is a built-in function to return the length of a list
...and "sys.argv" is just a list of command line arguments
The first argument is always the Python script filename
The second argument is supposed to be birthdate

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

Let's convert the birthdate input string into a datetime object


import sys
from datetime import datetime

if len(sys.argv) < 2:
    print("ERROR: Please provide a date")
else:
    BIRTHDAY = datetime.strptime(sys.argv[1], "%Y-%m-%d")
    message = "I am born on {}".format(BIRTHDAY.date())
    print(message)

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

Let's make sure that the date is formatted correctly:


import sys
from datetime import datetime

if len(sys.argv) < 2:
    print("ERROR: Please provide a date")
else:
    try:
        BIRTHDAY = datetime.strptime(sys.argv[1], "%Y-%m-%d")
    except ValueError:
        print("ERROR: Please enter a correct date")
        sys.exit()
    message = "I am born on {}".format(BIRTHDAY.date())
    print(message)

By the way: "sys.exit()" stops the program

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Exercise

Let's create a function that adds some years to a given date


import sys
from datetime import datetime, date

def get_future_date(base_date, years):
    future_date = date(
        base_date.year + years,
        base_date.month,
        base_date.day
    )
    return future_date

if len(sys.argv) < 3:
    print("ERROR: Please provide a date and an age")
else:
    try:
        birthday = datetime.strptime(sys.argv[1], "%Y-%m-%d")
    except ValueError:
        print("ERROR: Please enter a correct date")
        sys.exit()
    years = int(sys.argv[2])
    future_date = get_future_date(birthday, years)
    message = "I will turn {} on {}".format(years, future_date)
    print(message)

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Loops

You often need to repeat the same code in a loop
Loops look like this:


var my_list = [1, 2, 3, 4]

for my_number in my_list:
    if my_number == 1:
        continue
    print (my_number)

You can use "continue" to skip this iteration of the loop

Exercise

Let's extend the output of our program so that it shows all future birthdays up to the provided age


import sys
from datetime import datetime, date

def get_future_date(base_date, years):
    future_date = date(
        base_date.year + years,
        base_date.month,
        base_date.day
    )
    return future_date

if len(sys.argv) < 3:
    print("ERROR: Please provide a date and an age")
else:
    try:
        birthday = datetime.strptime(sys.argv[1], "%Y-%m-%d")
    except ValueError:
        print("ERROR: Please enter a correct date")
        sys.exit()
    years = int(sys.argv[2])
    years_list = range(1, years + 1, 1)
    for year in years_list:
        future_date = get_future_date(birthday, year)
        message = "I will turn {} on {}".format(year, future_date)
        print(message)

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?

Dictionaries

Dictionaries are so called "key-value-stores"
You can define an empty dictionary like this:
```
my_dict = {}
```
You can also define it with initial values:

my_dict = {
    "Martin": 33,
    "Eva": 24,
}

You can access an item by it's key:
```
martins_age = my_dict["Martin"]
```

Exercise

Let's add the final piece to our program
We will write a function that returns the weekday name for a given weekday number


import sys
from datetime import datetime, date

def get_weekday_name(weekday_number):
    weekdays = {
        1: "Monday",
        2: "Tuesday",
        3: "Wednesday",
        4: "Thursday",
        5: "Friday",
        6: "Saturday",
        7: "Sunday",
    }
    return weekdays[weekday_number]

def get_future_date(base_date, years):
    future_date = date(
        base_date.year + years,
        base_date.month,
        base_date.day
    )
    return future_date

if len(sys.argv) < 3:
    print("ERROR: Please provide a date and an age")
else:
    try:
        birthday = datetime.strptime(sys.argv[1], "%Y-%m-%d")
    except ValueError:
        print("ERROR: Please enter a correct date")
        sys.exit()
    years = int(sys.argv[2])
    years_list = range(1, years + 1, 1)
    for year in years_list:
        future_date = get_future_date(birthday, year)
        weekday = get_weekday_name(future_date.isoweekday())
        message = "I will turn {} on {}, {}".format(year, weekday, future_date)
        print(message)

Table of Content

Introduction
Python In A Nutshell
Cloud9 IDE
Variables
Strings
Input & Imports
The If-Statement & Type-casting
Datetimes
Exception Handling
Functions
Lists & Loops
Dictionaries
What's Next?