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Learn Python the Hard Way - Symbol Review Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Keywords

Keyword
Descri­ption
Example
 
and
Logical and
 
True and False == False
 
as
Part of the 
with-as
statement
 
with X as Y: pass
 
assert
Assert that something is true.
`assert False, "­Err­or!­"
 
break
Stop this loop right now.
 
while True: break
 
class
Define a class.
 
class Person­(ob­ject)
 
continue
Don't process more of the loop, do it again.
 
while True: continue
 
def
Define a function.
 
def X(): pass
 
del
Delete from dictio­nary.
 
del X[Y]
 
elif
Else if
 
if: X; elif: Y; else: J
 
else
Else condition
 
if: X; elif: Y; else: J
 
except
If an exception happens, do this.`
 
except ValueE­rror, e: print e
 
exec
Run a string as Python
 
exec 'print "­hel­lo"'
 
finally
Exceptions or not, finally do this no matter what.
 
finally: pass
 
for
Loop over a collection of things.
 
for X in Y: pass
 
from
Importing specific parts of a module.
 
from x import y
`
 
global
Declares a global variable
 
global X
 
if
If condition
 
if: X; elif: Y; else: J
 
import
Import a module into this one to use.
 
import os
 
in
Part of 
for-loops
. Also a test of X in Y.
 
for X in Y: pass
also 
1 in [1] == True
 
is
Like 
==
to test equality
1 is 1 == True
 
lambda
Create a short anonymous function
 
s = lambda y: y ** y; s(3)
 
not
Logical not
 
not True == False
 
or
Logical or
 
True or False == True
 
pass
This block is empty.
 
def empty(): pass
 
print
Print this string.
 
print 'this string'
 
raise
Raise an exception when things go wrong.
 
raise ValueE­rro­r("N­o")
 
return
Exit the function with a return value.
 
def X(): return Y
 
try
Try this block, and if exception, go to 
except
.
 
try: pass
 
while
While loop
 
while X: pass
 
with
With an expression as a variable do.
 
with X as Y: pass
 
yield
Pause here and return to caller.
 
def x(): yield Y; X().next()
 

Data Types

Type
Descri­ption
Example
 
True
True boolean value
 
True or False == True
 
False
False boolean value.
 
False and True == False
 
None
Represents "­not­hin­g" or "no value".
x = None
 
strings
Stores textual info
 
x = "­hel­lo"
 
numbers
Stores integers
 
i = 100
 
floats
Stores decimals
 
i = 10.389
 
lists
Stores a list of things
 
j = [1,2,3,4]
 
dicts
Stores a key=value mapping of things
e = {'x': 1, 'y': 2}

String Formats

Escape
Descri­ption
Example
 
%d
Decimal int
 
"­%d" % 45 == '45'
 
%o
Octal number
`%o % 1000 == '1750'
 
%u
Unsigned decimal
 
"­%u" % -1000 == '-1000'
 
%x
Hexade­cimal lowercase
 
"­%x" % 1000 == '3e8'
 
%X
Hexade­cimal uppercase.
 
"­%X" % 1000 == '3E8'
 
%e
Expone­ntial notation, lowercase 'e'.
 
"­%e" % 1000 == '1.000­000­e+03'
 
%E
Expone­ntial notation, uppercase 'E'.
 
"­%E" % 1000 == '1.000­000­E+03'
 
%f
Floating point real number.
 
"­%f" % 10.34 == '10.34­0000'
 
%F
Same as %f.
 
"­%F" % 10.34 == '10.34­0000'
 
%g
Either %f or %e, whichever is shorter.`
 
"­%g" % 10.34 == '10.34'
 
%G
Same as %g but uppercase.
 
"­%G" % 10.34 == '10.34'
 
%c
Character format.
 
"­%c" % 34 == '"'
 
%r
Repr format (debugging format).
 
"­%r" % int == "­<type 'int'>­"
 
%s
String format.
 
"%s there" % 'hi' == 'hi there'
 
%%
A percent sign.
 
"­%g%­%" % 10.34 == '10.34%'
 

String Escape Sequences

\\
Backslash
 
\'
Single­-quote
 
\''
Double­-quote
 
\a
Bell
 
\b
Backspace
 
\f
Formfeed
 
\n
 
Newline
 
\r
Carriage
 
\t
Tab
 
\v
Vertical tab