O'Reilly Book Excerpts: Python In a Nutshell; Learning Python, 2nd edition

A Python Quick Reference to Useful Commands

Editor's note: O'Reilly's Python books have been a staple source of quality information for programmers for years. If you haven't visited our Python Resource Center in a while, it may be time to stop by again. There you'll find two excellent resources: Learning Python, 3rd Edition and Python in a Nutshell, 2nd Edition. The former offers Python programmers a comprehensive learning tool for Python and object-oriented programming; the latter offers programmers one-stop shopping when they need help remembering or deciphering Python's syntax and its many modules.

In this excerpt, plucked from the pages of these two books, you'll find a quick reference to many useful Python commands, covering object methods, common file operations, and much more. And we've made it available for download as a PDF (55K) for you to print and post where you program. Enjoy.

OPERATOR PRECEDENCE IN EXPRESSIONS
Operator	Description	A
`expr,...`	String conversion	NA
{key:expr,...}	Dictionary creation	NA
[expr,...]	List creation	NA
(expr,...)	Tuple creation or simple parentheses	NA
f(expr,...)	Function call	L
x[index:index]	Slicing	L
x[index]	Indexing	L
x.attr	Attribute reference	L
x**y	Exponentiation (x to yth power)	R
~x	Bitwise NOT	NA
+x, -x	Unary plus and minus	NA
x*y, x/y, x//y, x%y	Multiplication, division, remainder	L
x+y, x-y	Addition, subtraction	L
x<<y, x>>y	Left-shift, right-shift	L
x&y	Bitwise AND	L
x^y	Bitwise XOR	L
x|y	Bitwise OR	L
x<y, x<=y, x>y, x>=y	Comparisons	C
x<>y, x!=y, x==y	Equality/inequality tests*	C
x is y, x is not y	Identity tests	C
x in y, x not in y	Membership tests	C
not x	Boolean NOT	NA
x and y	Boolean AND	L
x or y	Boolean OR	L
lambda arg,...: expr	Anonymous simple function	NA
* x!=y and x<>y are the same inequality test (!= is the preferred form, <> obsolete)
A – Associativity L – Left R – Right C – Chaining NA – Not associative

LIST OBJECT METHODS
Operator	Description
L.count(x)	Returns the number of occurrences of x in L
L.index(x)	Returns the index of the first occurrence of x in L or raises an exception if L has no such item
L.append(x)	Appends x to the end of L
L.extend(l)	Appends all the items of list l to the end of L
L.insert(i,x)	Inserts x at index i in L
L.remove(x)	Removes the first occurrence of x from L
L.pop(i=-1)	Returns the value of the item at index i and removes it from L
L.reverse( )	Reverses, in-place, the items of L
L.sort(f=cmp)	Sorts, in-place, the items of L, comparing items by f

COMMON FILE OPERATIONS
Operation	Interpretation
output = open('/tmp/spam', 'w')	Create output file ('w' means write).
input = open('data', 'r')	Create input file ('r' means read).
S = input.read( )	Read entire file into a single string.
S = input.read(N)	Read N bytes (1 or more).
S = input.readline( )	Read next line (through end-line marker).
L = input.readlines( )	Read entire file into list of line strings.
output.write(S)	Write string S into file.
output.writelines(L)	Write all line strings in list L into file.
output.close( )	Manual close (done for you when file collected).

COMMON DICTIONARY LITERALS AND OPERATIONS
Operation	Interpretation
D1 = { }	Empty dictionary
D2 = {'spam': 2, 'eggs': 3}	Two-item dictionary
D2['eggs']	Indexing by key
D2.has_key('eggs'),	'eggs' in D2 membership test
D2.keys( ), D2.values( ), D2.items( )	lists of keys, values, items
D2.copy( ), D2.update(D1)	shallow copy, dict merging
D2.get(key, default=None)	"indexing" w/default value
len(D1)	Length (number stored entries)
D2[key] = 42	Adding/changing
del D2[key]	deleting
D4 = dict(zip(keyslist, valslist))	Construction

COMMON TUPLE LITERALS AND OPERATIONS
Operation	Interpretation
( )	An empty tuple
T1 = (0,)	A one-item tuple (not an expression)
T2 = (0, 'Ni', 1.2, 3)	A four-item tuple
T2 = 0, 'Ni', 1.2, 3	Another four-item tuple (same as prior line)
T1[i]	Indexing
T1[i:j]	slicing
len(t1)	length (number of items)
T1 + T2	Concatenation
T2 * 3	repetition
for x in T2	Iteration
3 in T2	membership

---

View catalog information for Python In a Nutshell

View catalog information for Learning Python, 2nd Edition

Return to Python DevCenter.