Python For Kids For Dummies
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Programming is an important skill. Python will serve you well for years to come. The tables here give you the core words, built-ins, standard library functions, and operators that you'll use most when you're coding with Python.

Python Core Words

and Logical operator to test whether two things are both True. and

x>2 and x<10
as Assign a file object to a variable. Used with with.
Let your code refer to a module under a different name (also called an alias). Used with import.
with open(<name of file>,<file mode>) as <object name>:
import cPickle as pickle
break Stop execution of a loop. for i in range(10):
if i%2 ==0:
class Define a custom object. class <name of class>(object):
""Your docstring""
class MyClass(object):
""A cool function.""
continue Skip balance of loop and begin a new iteration. for i in range(10):
if i%2 ==0:
def Define a function. def <name of function>():
""Your docstring""
def my_function():
""This does... ""
elif Add conditional test to an if clause. See if.
else Add an alternative code block. See if.
for Create a loop which iterates through elements of a list (or other iterable). for <dummy variable name> in <sequence>:
for i in range(10):
from Import specific functions from a module without importing the whole module. from <module name> import <name of function or object>
from random import randint
global Make a variable global in scope. (If a variable is defined in the main section, you can change its value within a function.) global x
if Create a condition. If the condition is True, the associated code block is executed. Otherwise, any elif commands are processed. If there are none, or none are satisfied, execute the else block if there is one. if :

[elif :
, ...]
if x == 1:
print("x is 1")
elif x == 2:
print("x is 2")
elif x > 3:
print("x is greater than 3")
print("x is not greater than 3, nor is it 1 one or 2")
import Use code defined in another file without retyping it. import <name of module>
import random
in Used to test whether a given value is one of the elements of an object. 1 in range(10)
is Used to test whether names reference the same object. x = None
x is None # faster than
x == None
lambda Shorthand function definition. Usually used where a function needs to be passed as an argument to another function. lamda :

times = lambda x, y: x*y
command=lambda x: self.draw_line(self.control_points)
not Logical negation, used to negate a logical condition. Don't use for testing greater than, less than, or equal. 10 not in range(10)
or Logical operator to test whether at least one of two things is True. or

x<2 or x>10
pass Placeholder keyword. Does nothing but stop Python complaining that a code block is empty. for i in range (10):
print Output text to a terminal. print("Hello World!")
return Return from the execution of a function. If a value is specified, return that value, otherwise return None. return
return x+2
while Execute a code block while the associated condition is True. while :
while True:
with Get Python to manage a resource (like a file) for you. with open(,) as :

Extend Python's core functionality with these built-ins.

Python Built-ins
False Value, returned by a logical operation or directly assigned. ok_to_continue = False
age = 16
old_enough = age >=21
(evaluates comparison age>=21
and assigns the result to old_enough)
None Value used when representing the absence of a value or to initialise a variable which will be changed later. Returned by functions which do not explicitly return a value. x = None
True Value, returned by a logical operation. ok_to_continue = True
age = 16
old_enough = age >=21
(evaluates comparison age>=21
and assigns the result to old_enough)
__name__ Constant, shows module name. If it's not "__main__", the code is being used in an import. if __name__=="__main__":
dir List attributes of an item. dir(<object name>)
enumerate Iterate through a sequence and number each item. enumerate('Hello')
exit Exit Python (Command Line) interpreter. exit()
float Convert a number into a decimal, usually so that division works properly. 1/float(2)
getattr Get an attribute of an object by a name. Useful for introspection. getattr(<name of object>, <name of attribute>)
help Get Python docstring on object. help(<name of object>)
id Show the location in the computer's RAM where an object is stored. id(<name of object>)
int Convert a string into an integer number. int('0')
len Get the number of elements in a sequence. len([0,1])
object A base on which other classes can inherit from. class CustomObject(object):
open Open a file on disk, return a file object. open(, )
open('mydatafile.txt', 'r') # read
(opens a file to read data from)
open('mydatafile.txt', 'w') # write
(creates a new file to write to, destroys any existing file with the same name)
open('mydatafile.txt', 'a') # append
(adds to an existing file if any, or creates
a new one if none existing already)
print Reimplementation of print keyword, but as a function.
Need to import from the future to use it (srsly!)
from future import print_function
print ('Hello World!')
range Gives numbers between the lower and upper limits specified (including the lower, but excluding the upper limit). A step may be specified. range(10)
raw_input Get some text as a string from the user, with an optional prompt. prompt = 'What is your guess? '
players_guess = raw_input(prompt)
str Convert an object (usually a number) into a string (usually for printing). str(0)
type Give the type of the specified object. type(0)

Use the work that others have already done. Try these modules from the Python standard library.

Selected Functions from the Standard Library
ModuleWhat It DoesSample Functions/Objects
os.path Functions relating to files and file paths. os.path.exists()
pickle, cPickle Save and load objects to/from a file. pickle.load(), pickle.dump(, )
random Various functions relating to random numbers. random.choice(), random.randint(, ), random.shuffle()
String Stuff relating to strings. string.printable
sys Various functions related to your computer system. sys.exit()
Time Time-related functions. time.time()
Tkinter User interface widgets and associated constants. Tkinter.ALL

Add, subtract, divide, multiply, and more using these operators.

Python Operators
+ Plus Add two numbers.
Join two strings together.
Add: >>> 1+1
Join: >>> 'a'+'b'
Minus Subtract a number from another.
Can't use for strings.
>>> 1-1
* Times Multiply two numbers.
Make copies of a string.
Multiply: >>> 2*2
Copy: >>> 'a'*2
/ Divide Divide one number by another.
Can't use for strings.
1/2 # integer division:
Answer will be rounded down.
1/2.0 # decimal division
1/float(2) # decimal division
% Remainder (Modulo) Give the remainder when dividing the left number by the right number.
Formatting operator for strings.
>>> 10%3
** Power x**y means raise x to the power of y.
Can't use for strings.
>>> 3**2
= Assignment Assign the value on the right to the variable on the left. >>> a = 1
== Equality Is the left side equal to the right side? Is True if so; is False otherwise. >>> 1 == 1
>>> 'a' == 'a'
!= Not equal Is the left side not equal to the right side? Is True if so; is False otherwise. >>> 1 != 1
>>> 1 != 2
>>> 'a' != 'a'
> Greater than Is the left side greater than the right side?
>= means greater than or equal to
>>> 2 > 1
< Less than Is the left side less than the right side?
<= means less than or equal to
>>> 1 < 2
& (or and) And Are both left and right True?
Typically used for complex conditions where you want to do something if everything is True:
while im_hungry and you_have_food:
>>> True & True
>>> True and False
>>> True & (1 == 2)
| (or or) Or Is either left or right True?
Typically used for complex conditions where you want at least one thing to be True:
while im_bored or youre_bored:
>>> True | False
>>> True or False
>>> False | False
>>> (1 == 1) | False

About This Article

This article is from the book:

About the book author:

Brendan Scott is a dad who loves Python and wants kids to get some of its magic too. He started to help teach his oldest child to code. He maintains it to help other young people learn Python.

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