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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, 2nd Edition and Python in a Nutshell. 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.
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Related Reading |
| 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 |
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Showing messages 1 through 3 of 3.
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jython examples?
2005-02-10 07:43:15 dor [Reply | View]
Hi,
We are using jython in our project.
I wonder if all these data is applicabale for jython too, or not?
can you supply more data regarding jython.
D. Orbach
booksprice - one book one click best price -
jython examples?
2005-02-22 19:14:17 davidschein [Reply | View]
I believe Jython is current to CPython (AKA Python) version 2.1 and working on implementing 2.2/3. The O'Reilly titles are good at keep track of which features and libraries are available in which version.
www.jython.org is the place for answers. From that site:
"We will always strive to ensure that Jython remains as compatible with CPython as possible. Nevertheless, there are a number of differences between the two implementations that are unlikely to go away."
-
jython examples?
2005-02-26 11:48:00 dor [Reply | View]
Thanks a lot.
D. Orbach
books price - one book one click best price
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