Python cheatsheet

Implementation

• CPython (interpreter written in C)
• Cython (compiles to C)
• Jython (compiles to Java bytecode)
• IDLE

Print

• print("line\nline")
• print("line1", "line2", end="\n", sep="-")

Number

• 123, 0o173, 0x7b
• 0.4, .4
• 30000000, 3E8, 6.62E-34

String quote escaping

• "string\"string", 'string"string'
• 'string\'string', "string'string"

Type

• 2*3 is int, 2*3.0 is float, 2.0*3 is float, same for: ** / // % + -
• 6/2 is float
• 4 is int, 4.0 is float
• 2==2.0 is True

Integer division

• 6//4=1
• -6//4=-2

Operator priority

1. ! ~ + - (unary)
2. ** (right-sided binding)
3. */%
4. +- (binary)
5. << >>
6. < <= > >=
7. == !=
8. &
9. |
10. &&
11. ||
12. = += -= *= /= %= &= ^= |= >>= <<=

Comment

• # comment to the end of the line

Shortcut operator

• a += 1 is same as a = a+1
• same for any two-argument operator

Type conversion

• input("message") returns a string
• int(string), float(string), str(number)

String operator

• string + string (concatenation)
• string * number, number * string (repetition)

Condition

• if true_or_not: do_this_if_true
• elif true_or_not: do_this_if_true
• else: else_do_this

Loop

• while true_or_not: do_this_while_true
• else: always_executed
• for i in range(10): do_this
• else: always_executed
• for i in list:
• pass (empty instruction), break, continue

Range

• range(first included, last excluded, increment)
• range(10) = range(0, 10) = range(0, 10, 1)

List

• a sequence of data which can be scanned by the for loop
• list = name of a memory location where the list is stored
• list2 = list1 point to the same list, list2 = list1[:] is a copy
• list = [10, 5, 7], list[0] = 20, list[-1] = 3

List slicing

• list[start included : end excluded]
• list[-1:1] is same as []
• list[:end]
• list[start:] is same as list[start:len(list)]

List management

• len(list)
• list.append(4), list.insert(where, what), list.sort()
• del list[1], del list[1:3], del list[:] deletes all values, del list deletes the list
• elem in list, elem not in list
• for i in list:

List operator

• list1 + list2 (concatenation)
• list * number, number * list (repetition)

Multidimensional list

• row = ["a" for i in range(8)] is one dimension
• board = [["a" for i in range(8)] for j in range (8)] is two dimension, board[0][0]

Function

• def function():
• function and variable with same name forbidden
• def function(a, b, c, d=4), function(1, 2, 3, 4), function(c=3, a=1, b=2), function(1, c=3, b=2)
• return, return None, return 13, return list
• global var

Tuple

• a tuple is an immutable sequence type
• tuple = (1, 2, 3), tuple = 1, 2, 3
• tuple = (1,), tuple = 1, whereas var = (1) is not a tuple
• tuple = () is empty
• tuple[0], tuple[-1], tuple[1:], tuple[:-2]
• for i in tuple:

Tuple operator

• tuple1 + tuple2 (concatenation)
• tuple * number, number * tuple (repetition)
• v1, v2, v3 = v2, v3, v1

Dictionary

• an associative array
• key is unique, integer, float or string
• dict = {'dog': 'chien', 'horse': 'cheval', 'cat': 'chat'}
• {} is empty

Dictionary management

• len(dict)
• del dict['dog']
• for key in sorted(dict.keys()):
• for en,fr in dict.items():
• for fr in dict.values():

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PCAP: Programming Fundamentals in Python (Part 1), pythoninstitute.org.