Data Types
Integer |
-256, 15 |
Float |
-253.23, 1.253e-10 |
String |
"Hello", 'Goodbye', """Multiline""" |
Boolean |
True, False |
List |
[ value, ... ] |
Tuple |
( value, ... )1 |
Dictionary |
{ key: value, ... } |
Set |
{ value, value, ... }2 |
1 Parentheses usually optional
2 Create an empty set with set()
Statements
If Statement
if expression:
statements
elif expression:
statements
else:
statements
While Loop
while expression:
statements
For Loop
for var in collection:
statements
Counting For Loop
for i in range(start, end [, step]):
statements
(start is included; end is not) |
Arithmetic Operators
x + y |
add |
x - y |
subtract |
x * y |
multiply |
x / y |
divide |
x % y |
modulus |
x ** y |
xy |
Assignment shortcuts: x op= y
Example: x += 1 increments x
Comparison Operators
x< y |
Less |
x <= y |
Less or eq |
x > y |
Greater |
x >= y |
Greater or eq |
x == y |
Equal |
x != y |
Not equal |
Exception Handling
try:
statements
except [ exception type [ as var ] ]:
statements
finally:
statements |
|
|
Conversion Functions
int(expr) |
Converts expr to integer |
float(expr) |
Converts expr to float |
str(expr) |
Converts expr to string |
chr(num) |
ASCII char num |
String / List / Tuple Operations
len(s) |
length of s |
s[i] |
ith item in s (0-based) |
s[start : end] |
slice of s from start (included) to end (excluded) |
x in s |
True if x is contained in s |
x not in s |
True if x is not contained in s |
s + t |
the concatenation of s with t |
s * n |
n copies of s concatenated |
sorted(s) |
a sorted copy of s |
s.index(item) |
position in s of item |
More String Operations
s.lower() |
lowercase copy of s |
s.replace(old, new) |
copy of s with old replaced with new |
s.split( delim ) |
list of substrings delimited by delim |
s.strip() |
copy of s with whitespace trimmed |
s.upper() |
uppercase copy of s |
Mutating List Operations
del lst[i] |
Deletes ith item from lst |
lst.append(e) |
Appends e to lst |
lst.insert(i, e) |
Inserts e before ith item in lst |
lst.sort() |
Sorts lst |
Dictionary Operations
len(d) |
Number of items in d |
del d[key] |
Removes key from d |
key in d |
True if d contains key |
d.keys() |
Returns a list of keys in d |
Function Definitions
def name(arg1, arg2, ...):
statements
return expr |
|
|
Environment
sys.argv |
List of command line arguments (argv[0] is executable) |
os.environ |
Dictionary of environment variables |
os.curdir |
String with path of current directory |
import sys; print(sys.argv) or
from sys import argv; print(argv)
String Formatting
"Hello, {0} {1}".format("abe", "jones")
Hello, abe jones
"Hello, {fn} {ln}".format(fn="abe", ln="jones")
Hello, abe jones
"You owe me ${0:,.2f}".format(253422.3)
You owe me $253,422.30
now = datetime.now()
'{:%Y-%m-%d %H:%M:%S}'.format(now)
2012-05-16 15:04:33 |
Useful Functions
exit( code ) |
Terminate program with exit code |
raw_input("prompt") |
Print prompt and readline() from stdin1 |
1 Use input("prompt") in Python 3
Code Snippets
Loop Over Sequence
for index, value in enumerate(seq):
print("{} : {}".format(index, value))
Loop Over Dictionary
for key in sorted(dict):
print(dict[key])
Read a File
with open("filename", "r") as f:
for line in f:
line = line.rstrip("\n") # Strip newline
print(line) |
|
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Comments
Amazing cheatsheet.
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