Some Python Grammar

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Some Basic Grammar

1.Built-In Types and Data Structures

2.Control Flow

  • if Statements 

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    if x < 0:
        print("x < 0")
    elif x == 0:
        print("x==0")
    else:
        print("x > 0")

  • for Statements 

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    >>> for w in words[:]:  # Loop over a slice copy of the entire list.
    ...     if len(w) > 6:
    ...         words.insert(0, w)
    ...
    >>> words
    ['defenestrate', 'cat', 'window', 'defenestrate']

  • range() Function 

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    >>> for i in range(3):
    ...     print(i)
    ...
    0
    1
    2
    >>> list(range(5))
    [0, 1, 2, 3, 4]

  • break and continue Statements, and else Clauses on Loops The else Clauses is executed when the loop terminates through exhaustion of the list (with for) or when the condition becomes false (with while), but not when the loop is terminated by a break statement.

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>>> for n in range(2, 5):
...     for x in range(2, n):
...         if n % x == 0:
...             print(n, 'equals', x, '*', n//x)
...             break
...     else:
...         # loop fell through without finding a factor
...         print(n, 'is a prime number')
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
  • Defining Functions
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>>> def fib(n):    # write Fibonacci series up to n
...     """Print a Fibonacci series up to n."""
...     a, b = 0, 1
...     while a < n:
...         print(a, end=' ')
...         a, b = b, a+b
...     print()
...
>>> # Now call the function we just defined:
... fib(2000)
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597
#---------------------------------------------------------
# parameter passing
def foo(a, b):
    "parameter passing in function"
    print(">>>parameter passing")
    print("addr(a) = {:#X}, addr(b) = {:#X}".format(id(a), id(b)))
    a = 2
    b.append(1)
    print(">>>assignments")
    print("addr(a) = {:#X}, addr(b) = {:#X}".format(id(a), id(b)))

c = 1
d = [12]
print(">>>before")
print("addr(c) = {:#X}, addr(d) = {:#X}".format(id(c), id(d)))
foo(c, d)
print(">>>after")
print("c = {0}, d = {1}".format(c, d))

>>>before
addr(c) = 0X560BA944AE80, addr(d) = 0X7F9D78C13108
>>>parameter passing
addr(a) = 0X560BA944AE80, addr(b) = 0X7F9D78C13108
>>>assignments
addr(a) = 0X560BA944AEA0, addr(b) = 0X7F9D78C13108
>>>after
c = 1, d = [12, 1]