python tutorial - World Colleges Information
A Caffeinated Crash Course in Python
Python is not…. • Java • C • Perl
The Python Interpreter • Type “python” at the command prompt • In windows, find the python icon on the start menu
Dir and Help help()
dir()
Syntax Errors • Python Errors show the line number of the error • Check the line above if your error makes no sense
White Space
String Basics • Not a mutable data type
• String can be delimited with either the “ or ‘
More Strings • Concatenation uses the +
• You can do math with strings!
Output
Indexing • To index into a string, specify the position inside square brackets
• You can index into a string from the “end” of the string.
Slicing • A Substring of a string is a slice
• Your head or tail can be a negative index
More Slicing • You don’t need to specify the beginning and end of the string
• Find the length of a string with len()
Example
Lists • Lists in python are made of any data type delimited by commas and surrounded by brackets.
• Lists are mutable
More on Lists • You can index into lists
• You can slice lists
Modifying Lists • You can add lists
• And append to them
List Methods
• sort - sorts the list in place, returns nothing • sorted - does not modify the list, returns new sorted list • reverse - reverses the list in place, returns nothing
String Formatting
• The % operator substitutes values into a string • %s and %d are placeholders for the values (%d makes sure it’s a number) • “%s has %d letters” % (“colorless”, len(“colorless”)) becomes the string “colorless has 9 letters”
Converting from Strings to Lists • Join a list to make a string
• Split a string to make a list
For and If • If statements
• For Statements
List Comprehensions • Applies a function to every element of a list
Dictionaries • Hash - maps things to things!
Even More Dictionaries
Example: Letter Frequencies
Classes
Importing and the Python path • Import using the import command • You can import everything from a module using the syntax “from <module> import *”
Files Filename = “/home/havasi/input.txt” input = open(Filename, ‘r’) output = open(Filename + ‘.out’, ‘w’) for line in input.readlines(): input.write(‘Cows! \n’) input.close() output.close()
Resources • Python.org • NLTK Python Tutorial – http://nltk.org/doc/en/programming.html
• IDLE (Windows Development Env.) – http://www.python.org/idle/
Python is not…. • Java • C • Perl
The Python Interpreter • Type “python” at the command prompt • In windows, find the python icon on the start menu
Dir and Help help()
dir()
Syntax Errors • Python Errors show the line number of the error • Check the line above if your error makes no sense
White Space
String Basics • Not a mutable data type
• String can be delimited with either the “ or ‘
More Strings • Concatenation uses the +
• You can do math with strings!
Output
Indexing • To index into a string, specify the position inside square brackets
• You can index into a string from the “end” of the string.
Slicing • A Substring of a string is a slice
• Your head or tail can be a negative index
More Slicing • You don’t need to specify the beginning and end of the string
• Find the length of a string with len()
Example
Lists • Lists in python are made of any data type delimited by commas and surrounded by brackets.
• Lists are mutable
More on Lists • You can index into lists
• You can slice lists
Modifying Lists • You can add lists
• And append to them
List Methods
• sort - sorts the list in place, returns nothing • sorted - does not modify the list, returns new sorted list • reverse - reverses the list in place, returns nothing
String Formatting
• The % operator substitutes values into a string • %s and %d are placeholders for the values (%d makes sure it’s a number) • “%s has %d letters” % (“colorless”, len(“colorless”)) becomes the string “colorless has 9 letters”
Converting from Strings to Lists • Join a list to make a string
• Split a string to make a list
For and If • If statements
• For Statements
List Comprehensions • Applies a function to every element of a list
Dictionaries • Hash - maps things to things!
Even More Dictionaries
Example: Letter Frequencies
Classes
Importing and the Python path • Import using the import command • You can import everything from a module using the syntax “from <module> import *”
Files Filename = “/home/havasi/input.txt” input = open(Filename, ‘r’) output = open(Filename + ‘.out’, ‘w’) for line in input.readlines(): input.write(‘Cows! \n’) input.close() output.close()
Resources • Python.org • NLTK Python Tutorial – http://nltk.org/doc/en/programming.html
• IDLE (Windows Development Env.) – http://www.python.org/idle/
