basics copyright software carpentry 2010 this work is licensed under the creative commons...

Basics

Copyright © Software Carpentry 2010This work is licensed under the Creative Commons Attribution LicenseSee http://software-carpentry.org/license.html for more information.

Python

Python Basics

A simple interpreted language

Python Basics

A simple interpreted language no separate compilation step

Python Basics

$ python>>>

A simple interpreted language no separate compilation step

Python Basics

$ python>>> print 1 + 23>>>

A simple interpreted language no separate compilation step

Python Basics

$ python>>> print 1 + 23>>> print 'charles' + 'darwin'charlesdarwin>>>

A simple interpreted language no separate compilation step

Python Basics

Put commands in a file and execute that

Python Basics

Put commands in a file and execute that$ nano very-simple.py

Python Basics

Put commands in a file and execute that$ nano very-simple.py

print 1 + 2print 'charles' + 'darwin'

Python Basics

Put commands in a file and execute that$ nano very-simple.py

print 1 + 2print 'charles' + 'darwin'

$ python very-simple.py3charlesdarwin$

Python Basics

Use an integrated development environment (IDE)

Python Basics

Use an integrated development environment (IDE)

Sourcefile

Python Basics

Use an integrated development environment (IDE)

Sourcefile

Executionshell

Python Basics

Variables are names for values

Python Basics

Variables are names for valuesCreated by use

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

>>> planet = 'Pluto'>>>

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

>>> planet = 'Pluto'>>> print planetPluto>>>

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

variable value

planet 'Pluto'

>>> planet = 'Pluto'>>> print planetPluto>>>

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

>>> planet = 'Pluto'>>> print planetPluto>>> moon = 'Charon'>>>

variable value

planet

moon

'Pluto'

'Charon'

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

>>> planet = 'Pluto'>>> print planetPluto>>> moon = 'Charon'>>> p = planet>>>

variable value

planet

moon

'Pluto'

'Charon'

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

>>> planet = 'Pluto'>>> print planetPluto>>> moon = 'Charon'>>> p = planet>>>

variable value

planet

moon

p

'Pluto'

'Charon'

Python Basics

Variables are names for valuesCreated by use: no declaration necessary

>>> planet = 'Pluto'>>> print planetPluto>>> moon = 'Charon'>>> p = planet>>> print pPluto>>>

variable value

planet

moon

p

'Pluto'

'Charon'

Python Basics

A variable is just a name

Python Basics

A variable is just a nameDoes not have a type

Python Basics

A variable is just a nameDoes not have a type>>> planet = 'Pluto'>>>

Python Basics

A variable is just a nameDoes not have a type>>> planet = 'Pluto'>>> planet 'Pluto'

variable value string

Python Basics

A variable is just a nameDoes not have a type>>> planet = 'Pluto'>>> planet = 9>>> planet 'Pluto'

9

variable value

integer

Python Basics

A variable is just a nameDoes not have a type>>> planet = 'Pluto'>>> planet = 9>>> planet 'Pluto'

9

variable value

Values are garbage collected

Python Basics

A variable is just a nameDoes not have a type>>> planet = 'Pluto'>>> planet = 9>>> planet 'Pluto'

9

variable value

Values are garbage collected

If nothing refers to data any longer, it can be recycled

Python Basics

A variable is just a nameDoes not have a type>>> planet = 'Pluto'>>> planet = 9>>> planet 'Pluto'

9

variable value

Values are garbage collected

If nothing refers to data any longer, it can be recycled

Python Basics

Must assign value to variable before using it

Python Basics

Must assign value to variable before using it>>> planet = 'Sedna'>>>

Python Basics

Must assign value to variable before using it>>> planet = 'Sedna'>>> print plant # note the deliberate misspelling

Python Basics

Must assign value to variable before using it>>> planet = 'Sedna'>>> print plant # note the deliberate misspellingTraceback (most recent call last): print plantNameError: name 'plant' is not defined>>>

Python Basics

Must assign value to variable before using it

Python does not assume default values for variables

>>> planet = 'Sedna'>>> print plant # note the deliberate misspellingTraceback (most recent call last): print plantNameError: name 'plant' is not defined>>>

Python Basics

Must assign value to variable before using it

Python does not assume default values for variablesDoing so can mask many errors

>>> planet = 'Sedna'>>> print plant # note the deliberate misspellingTraceback (most recent call last): print plantNameError: name 'plant' is not defined>>>

Python Basics

Must assign value to variable before using it

Python does not assume default values for variablesDoing so can mask many errorsAnything from # to the end of the line is a comment

>>> planet = 'Sedna'>>> print plant # note the deliberate misspellingTraceback (most recent call last): print plantNameError: name 'plant' is not defined>>>

Python Basics

Values do have types

Python Basics

Values do have types>>> string = "two">>> number = 3>>> print string * number # repeated concatenationtwotwotwo>>>

Python Basics

Values do have types>>> string = "two">>> number = 3>>> print string * number # repeated concatenationtwotwotwo>>> print string + numberTraceback (most recent call last) number + stringTypeError: cannot concatenate 'str' and 'int' objects>>>

Python Basics

Values do have types>>> string = "two">>> number = 3>>> print string * number # repeated concatenationtwotwotwo>>> print string + numberTraceback (most recent call last) number + stringTypeError: cannot concatenate 'str' and 'int' objects>>>

Would probably be safe here to produce 'two3'

Python Basics

Values do have types>>> string = "two">>> number = 3>>> print string * number # repeated concatenationtwotwotwo>>> print string + numberTraceback (most recent call last) number + stringTypeError: cannot concatenate 'str' and 'int' objects>>>

Would probably be safe here to produce 'two3'But then what should '2'+'3' be?

Python Basics

Values do have types>>> string = "two">>> number = 3>>> print string * number # repeated concatenationtwotwotwo>>> print string + numberTraceback (most recent call last) number + stringTypeError: cannot concatenate 'str' and 'int' objects>>>

Would probably be safe here to produce 'two3'But then what should '2'+'3' be?Doing too much is as bad as doing too little…

Python Basics

Use functions to convert between types

Python Basics

Use functions to convert between types>>> print int('2') + 35>>>

Python Basics

Use functions to convert between types>>> print int('2') + 35>>> print 2 + str(3)23>>>

Python Basics

Numbers

Python Basics

Numbers14 32-bit integer

(on most machines)

Python Basics

Numbers14 32-bit integer

(on most machines)14.0 64-bit float

(ditto)

Python Basics

Numbers14 32-bit integer

(on most machines)14.0 64-bit float

(ditto)1+4j complex number

(two 64-bit floats)

Python Basics

Numbers14 32-bit integer

(on most machines)14.0 64-bit float

(ditto)1+4j complex number

(two 64-bit floats)x.real, x.imag

real and imaginary parts of complex number

Python Basics

Arithmetic

Python Basics

ArithmeticAddition + 35 + 22 57

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13Multiplication * 3 * 2 6

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13Multiplication * 3 * 2 6

'Py' * 2 'PyPy'

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13Multiplication * 3 * 2 6

'Py' * 2 'PyPy'Division / 3.0 / 2 1.5

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13Multiplication * 3 * 2 6

'Py' * 2 'PyPy'Division / 3.0 / 2 1.5

3 / 2 1

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13Multiplication * 3 * 2 6

'Py' * 2 'PyPy'Division / 3.0 / 2 1.5

3 / 2 1Exponentiation

** 2 ** 0.5 1.41421356...

Python Basics

ArithmeticAddition + 35 + 22 57

'Py' + 'thon'

'Python'

Subtraction - 35 - 22 13Multiplication * 3 * 2 6

'Py' * 2 'PyPy'Division / 3.0 / 2 1.5

3 / 2 1Exponentiation

** 2 ** 0.5 1.41421356...

Remainder % 13 % 5 3

Python Basics

Prefer in-place forms of binary operators

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>>

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>> years += 1>>>

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>> years += 1>>>

The same as years = years + 1

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>> years += 1>>> print years501>>>

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>> years += 1>>> print years501>>> years %= 10>>>

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>> years += 1>>> print years501>>> years %= 10>>>

The same as years = years % 10

Python Basics

Prefer in-place forms of binary operators>>> years = 500>>> years += 1>>> print years501>>> years %= 10>>> print years5>>>

Python Basics

Comparisons

Python Basics

Comparisons3 < 5 True

Python Basics

Comparisons3 < 5 True3 != 5 True

Python Basics

Comparisons3 < 5 True3 != 5 True3 == 5 False

Python Basics

Comparisons3 < 5 True3 != 5 True3 == 5 False Single = is assignment

Double == is equality

Python Basics

Comparisons3 < 5 True3 != 5 True3 == 5 False3 >= 5 False

Python Basics

Comparisons3 < 5 True3 != 5 True3 == 5 False3 >= 5 False1 < 3 < 5 True

Python Basics

Comparisons3 < 5 True3 != 5 True3 == 5 False3 >= 5 False1 < 3 < 5 True1 < 5 > 3 True But please don't

do this

Python Basics

Comparisons3 < 5 True3 != 5 True3 == 5 False3 >= 5 False1 < 3 < 5 True1 < 5 > 3 True3+2j < 5 error

October 2010

created by

Greg Wilson

Copyright © Software Carpentry 2010This work is licensed under the Creative Commons Attribution LicenseSee http://software-carpentry.org/license.html for more information.