Python
What you should know about it!
What is Python?
- Interpreted: Do not need to compile your program before executing
- Interactive: Can sit at a prompt and interact with the interpreter directly
- Object-Oriented: Style of programming that encapsulates code within objects
About Python
- Developed by Guido van Rossum in 1989
- It is FREE!!
- Designed to be fun to use and easy to learn
- Named after
Monty Python's Flying Circus
Installing Python
Installing Python
The best way (in my opinion) to install Python is through Anaconda
https://www.anaconda.com/download/#macos
Installing Python
- Go to https://www.anaconda.com/download/#macos
- Download the corresponding installation file for Python 3.6
- Read the documentation in "How to Install ANACONDA" and follow instructions
- For command-line, use:
bash /path/to/file/Anaconda3-5.2.0-Linux-x86_64.sh - And now follow the instructions.
Installing Python
Once you've installed Python correctly, you shold be able to
- Open up the Terminal app
- Type
ipython - And begin with an interactive Python session
victor2@Victors-MBP-3:~ ipython
Python 3.6.4 |Anaconda custom (64-bit)| (default, Jan 16 2018, 12:04:33)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.2.1 -- An enhanced Interactive Python. Type '?' for help.
In [1]:
Installing Python
For more information on how to install Python
see:
Interactive Session
- To begin an interactive Python session, type
pythonoripythonon the command line:
victor2@Victors-MBP-3:~ ipython
Python 3.6.4 |Anaconda custom (64-bit)| (default, Jan 16 2018, 12:04:33)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.2.1 -- An enhanced Interactive Python. Type '?' for help.
In [1]:
Interactive Session
- To exit an interactive Python session, type:
Ctrl-d, exit()orquit()
victor2@Victors-MBP-3:~ ipython
Python 3.6.4 |Anaconda custom (64-bit)| (default, Jan 16 2018, 12:04:33)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.2.1 -- An enhanced Interactive Python. Type '?' for help.
In [1]: exit
victor2@Victors-MBP-3:~
Assignment
- You can assing values to variables with
<var> = <expression>
victor2@Victors-MBP-3:~ ipython
nuPython 3.6.4 |Anaconda custom (64-bit)| (default, Jan 16 2018, 12:04:33)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.2.1 -- An enhanced Interactive Python. Type '?' for help.
In [1]: number = 5
In [2]: number
Out[2]: 5
Assignment
- Variables can be reassigned. Python will retain the most recent assignment.
- For example: swap values of
xandy
In [1]: x = 5
In [2]: x
Out[2]: 5
In [3]: y = 12
In [4]: y
Out[4]: 12
In [5]: x = y
In [6]: y = x
In [7]: x, y
Out[7]: (12, 12)
Assignment
- Variables can be reassigned. Python will retain the most recent assignment.
- For example: swap values of
xandy
In [1]: x = 5
In [2]: x
Out[2]: 5
In [3]: y = 12
In [4]: y
Out[4]: 12
In [5]: temp = x
In [6]: x = y
In [7]: y = temp
In [8]: x, y
Out[7]: (12, 5)
Multiple assignment
- You can assing values to multiple variables with
<var1>, <var2>, ... = <expr1>, <expr2>, ...
In [1]: x, y = 5, 12
In [2]: x
Out[2]: 5
In [3]: y
Out[3]: 12
Multiple Assignment
- Variables can be reassigned. Python will retain the most recent assignment.
- For example: swap values of
xandy
In [1]: x, y = 5, 12
In [2]: x, y = y, x
In [3]: x,y
Out[3]: (12, 5)
Input & Output
- Ask for input from command-line with
input:
In [1]: name = input("What is your name?")
What is your name?"Victor"
In [2]: print("Hello", name)
Hello "Victor"
name.Operators
Mathematical
| + | Additon |
| - | Subtraction |
| * | Multiplicaiton |
| / | Divison |
| ** | Exponents |
| % | Remainder |
| abs() | Absolute value |
Operators
Relational
| == | Equal to |
| != | Not equal to |
| > | Greater than |
| < | Less than |
| ≥ | Greather than or equal to |
| ≤ | Less than or equal to |
Operators
Logical
| and | Logical 'and' |
| or | Logical 'or' |
Operators
Examples
In [1]: 2 + 2 * 3
Out[1]: 8
In [2]: (2 + 2) * 3
Out[2]: 12
In [3]: 3.1415 * 2
Out[3]: 6.283
In [4]: 5/2
Out[4]: 2.5
In [5]: 2**100
Out[5]: 1267650600228229401496703205376
Data Types
Data Types - String
- Immutable sequence of characters
- Examples:
Spam,eggs, andspam and eggs
In [1]: S = "Spam"
Data Types - String
- To get the length f a string, use:
len(string_name)
In [1]: S = "Spam"
In [2]: len(S)
Out[2]: 4
Data Types - String
- Indexing: items are ordered left-to-right, beginning with 0
string_name[index]
In [1]: S = "Spam"
In [2]: len(S)
Out[2]: 4
In [3]: S[0]
Out[3]: 'S'
In [4]: S[2]
Out[4]: 'a'
In [5]: S[-1]
Out[5]: 'm'
Data Types - String
- Slicing: Extracts whole sections
string_name[begin:end]
Try: S[1:3]
In [1]: S = "Spam"
In [2]: len(S)
Out[2]: 4
In [3]: S[1:3]
Out[3]: 'pa'
Data Types - String
- Concatenation: join two string with "
+" - Repetition: repeat a string with "
*"
Try: S[1:3]
In [1]: S = "Spam"
In [2]: len(S)
Out[2]: 4
In [3]: S + 'Eggs'
Out[3]: 'SpamEggs'
In [4]: S * 4
Out[4]: 'SpamSpamSpamSpam'
Data Types - Lists
- Indexing and slicing - Just like strings
- Try:
L[1]andL[0:-1]
In [1]: L = [1, 'spam', 4.0, 'U']
In [2]: L
Out[2]: [1, 'spam', 4.0, 'U']
In [3]: L[1]
Out[3]: 'spam'
In [4]: L[0:-1]
Out[4]: [1, 'spam', 4.0]
Data Types - Lists
- Can grow and shrink on command
- Try:
L.append('eggs')andL[3]
In [1]: L = [1, 'spam', 4.0, 'U']
In [2]: L
Out[2]: [1, 'spam', 4.0, 'U']
In [5]: L.append('eggs')
In [6]: L
Out[6]: [1, 'spam', 4.0, 'U', 'eggs']
In [7]: del L[3]
In [8]: L
Out[8]: [1, 'spam', 4.0, 'eggs']
Data Types - Lists
- Can create multidimensional lists
- Start with an empty list
In [1]: M = []
Data Types - Lists
- Can create multidimensional lists
- Add a new list:
[1, 2, 3]
In [1]: M = []
In [2]: M.append([1, 2, 3])
In [3]: M
Out[3]: [[1, 2, 3]]
Data Types - Lists
- Can create multidimensional lists
- Add another list:
[4, 5, 6]
In [1]: M = []
In [2]: M.append([1,2,3])
In [3]: M
Out[3]: [[1, 2, 3]]
In [4]: M.append([4, 5, 6])
In [5]: M
Out[5]: [[1, 2, 3], [4, 5, 6]]
Data Types - Lists
- Can create multidimensional lists
- Index the list. Try extracting the 3
In [1]: M = []
In [2]: M.append([1,2,3])
In [3]: M
Out[3]: [[1, 2, 3]]
In [4]: M.append([4, 5, 6])
In [5]: M
Out[5]: [[1, 2, 3], [4, 5, 6]]
In [6]: M[0][2]
Out[6]: 3
Data Types - Lists
- Lists are dynamic and heterogeneous.
- Don't need to allocate space, and can mix types!
In [1]: A = []
In [2]: A.append([1, 2, 3])
In [3]: A
Out[3]: [[1, 2, 3]]
In [4]: A.append(['spam', 'eggs'])
In [5]: A
Out[5]: [[1, 2, 3], ['spam', 'eggs']]
In [6]: A.append([4.0, 'spam', [1, 2, 'string'], 5])
In [7]: A
Out[7]: [[1, 2, 3], ['spam', 'eggs'], [4.0, 'spam', [1, 2, 'string'], 5]]
Data Types - Tuples
- Like lists, but immutable!
- Example:
(1, 'spam', 4.0, 'U')
In [1]: T = (1, 'spam', 4.0, 'U')
Data Types - Tuples
- Length, concatenation, Indexing
- Try:
len(T); T + (5,6); T[1]
In [1]: T = (1, 'spam', 4.0, 'U')
In [2]: len(T)
Out[2]: 4
In [3]: T + (5,6)
Out[3]: (1, 'spam', 4.0, 'U', 5, 6)
In [4]: T[1]
Out[4]: 'spam'
Data Types - Tuples
- Change or remove elements
- Try:
del T[2]
In [1]: T = (1, 'spam', 4.0, 'U')
In [2]: len(T)
Out[2]: 4
In [3]: T + (5,6)
Out[3]: (1, 'spam', 4.0, 'U', 5, 6)
In [4]: T[1]
Out[4]: 'spam'
In [5]: del T[2]
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-5-9678804ef101> in <module>()
----> 1 del T[2]
TypeError: 'tuple' object doesn't support item deletion
Data Types - Dictionaries
- Mutable key-value pairs
- Example:
{'food': 'spam, 'color': 'pink', 'quantity': 4}
In [1]: D = {'food': 'spam', 'color': 'pink', 'quantity': 4}
Data Types - Dictionaries
- Index with keyword
- Try:
D['food']
In [1]: D = {'food': 'spam', 'color': 'pink', 'quantity': 4}
In [2]: D['food']
Out[2]: 'spam'
Data Types - Dictionaries
- Change values
- Try:
D['quantity'] += 1
In [1]: D = {'food': 'spam', 'color': 'pink', 'quantity': 4}
In [2]: D['food']
Out[2]: 'spam'
In [3]: D['quantity'] += 1
In [4]: D
Out[4]: {'color': 'pink', 'food': 'spam', 'quantity': 5}
Conditional Statements
if conditon_1
do something
elif conditon_2:
do something else
else:
do thing number 3
Example of a script
>>> spam = input(“2 letter word for (and rhymes with) you & me: “) >>> guido = [spam, ‘eggs’]
>>> if guido[1] == ‘eggs’:
guido[1] = ‘are the’ >>> x = guido
>>> sausage = input(“Like a time of day, but begins with ‘k’: “)
>>> y = sausage + ‘s’
>>> bacon = input(“Fill in the blank in this children’s game: Simon ____: “) >>> z = [‘who’, bacon[0:-1]]
>>> print( x, y, z, “Ni!”)
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