Sintassi di base di Python (con esempi)

# assign the integer 1 to the variable i (also "creates" the variable")
i = 1

# assign the string "foobar" to the variable s
s = "foobar"

# Add 5 to the integer i - this is equivalent to i = i + 5
i += 5
# i now holds the integer 6.

# Try to add i and s - this will throw an exception when executed
# TypeError: unsupported operand type(s) for +: 'int' and 'str'
result = i + s

# variables can also be "undeclared" by deleting them.
# Further access to the variable i will throw a NameError exception,
# as the variable does not exist any more.
del i

i += 5 # now throws an exception: NameError: name 'i' is not defined

from __future__ import print_function

i = 1
print(i)

j = 0x1234   # hex number, is 16#1234 in IEC and 4660 in decimal
k = 0o123    # octal number, is 8#123 in IEC and 83 decimal
l = 0b101010 # binary number, is 2#101010 in IEC and 42 in decimal
print(j, k, l)

m = (2 + 3)*10 # k is 50 now
print(m)

n = 10 ** 100 # 10 to the power of 100
print(n)

Uscita risultante:

# A simple float...
a = 123.456

# A float containing the integral value 2
b = 2.

# Leading zeroes can be left off
c = .3 # same as 0.3

# Exponential / scientific representation
d = -123e-5

# booleans behave like integers, except when converted to strings.
# The built-in function "type" can be used to query the type of a value.
print("True:  ", True, type(True))
print("False: ", False, type(False))
print("1:     ", 1, type(1))
print("False + 0: ", False + 0, type(False + 0))
print("True * 5: ", True * 5, type(True * 5))

Uscita risultante:

# encoding:utf-8
from __future__ import print_function

a = "a simple string"
b = 'another string'
c = "strings may contain 'quotes' of the other type."
d = "multiple string literals" ' are concatenated ' '''by the parser'''
e = "Escaping: quotes: \" \' backslash: \\ newline: \r\n ascii code: \x40"
f = """triple-quoted strings may contain newlines, "single"
'quotes' and '''multiquotes''' of the other type"""
g = "Üňíçǿđȩ is also possible: 北京, Москва, Αθήνα, القاهرة"
h = r"c:\raw\strings\retain\backslashes.txt"

# we iterate over a sequence of all the variables defined above:
for i in (a,b,c,d,e,f,g,h):
    print(i) # prints the contents of the variable

Uscita risultante:

from __future__ import print_function
print("Testing tuples and lists")

# We define a tuple with the numbers from 1 to 10:
t = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print("Tuple:", t)

# We can access the 6th element of the tuple.
# As in C, index counting starts with 0.
print("Element 5:", t[5])

# Subscription is more powerful using the range syntax:
print("Range[2:5]:", t[2:5]) # lower bound is inclusive, upper bound is exclusive.
print("Range[2::2]:", t[2::2]) # start with 3rd element, and print every 2nd element.
print("Range[-3:-1]:", t[-3:-1]) # Start with the 3rd last element, end just before the last element (upper bound is exclusive)
print("Range[::-1]:", t[::-1]) # negative step with - print backwards

# lists are similar to tuples...
l = [11, 12, 13, "8", t] # contains mixed types: 3 integers, a string, and the tuple defined above.
print("List:", l)

# ... but elements can be added or removed dynamically.
l.append(9) # Add a 9 to the list.
print("List with 9:", l)
print("List Range[3:6:2]:", l[3:6:2]) # print the 4th and 6th element.

del l[1] # remove the element at index 1, the 12.
print("Removed[1]:", l)
del l[1:3] # Remove the elements at index 1 and 2, the 13 and the '8'.
print("Removed[1:3]:", l)

Uscita risultante:

from __future__ import print_function
print("Testing dictionaries")

# Declare a dictionary with three entries, the third being a list
d = {1: "a", 2: "b", "my list": [1, 2, 3]}
print(d)

# print the value of the key 1
print(d[1])

# remove the value with the key "my list"
del d["my list"]

# Add a value 4 with the key 3
d[3] = 4
print(d)

# The "get" method returns the second argument if the key cannot be found.
print(d.get(1, 42))
print(d.get(23, 42))

# print all keys in the dictionary
for key in d:
    print(key)

# index access for unknown keys will throw a "KeyError" exception!
print(d[23])

Uscita risultante:

E poi nell'ultima riga, lo script termina:

Clicca il Particolari pulsante per visualizzare la traccia dello stack. Qui si determina il numero di riga 27 e la chiave sconosciuta 23.