3) Structures de contrôle

Affectations, entrées, sorties

a = 2
b, c, d = 3, "oui", 12
a, b = b, a
print(a, b, c, d)

3 2 oui 12

dépaquetage de tuples

T = (1,2,3,4)
a, b, c, d = T
print(a,b,c,d)

1 2 3 4

a = input("entrer la valeur de a : ") (ne marche pas avec le Notebook)

a = 2
b = 3
c = a+b
print("on trouve", a, "+", b ,"=", c)

on trouve 2 + 3 = 5

Instruction conditionnelle : if, elif, else

n = 1
if n == 0:
    print("n=0")

n=1
if n == 0:
    print("n=0")
else:
    print("n<>0")        

n<>0

n = 25
if n%3 == 0:
    print(0)
elif n%3 == 1:
    print(1)
else:
    print(2)  

1

Boucles

while

i=1
while i < 5:
    print(i**2)
    i = i+1

1
4
9
16

i=1
while i < 100:
    print(i**2)
    i = i+1
    if i>4:
        break

1
4
9
16

def f():
    i=1
    while i < 100:
        print(i**2)
        i = i+1
        if i>4:
            return

f()

1
4
9
16

for

for i in range(5):
    print(i)

0
1
2
3
4

S="Bonjour les MP"
for i in S:
    print(i)

B
o
n
j
o
u
r
 
l
e
s
 
M
P

T=(1,2,3,4,5)
for i in T:
    print(i)

1
2
3
4
5

L=[1,2,3,4]
for i in L:
    print(i)

1
2
3
4

D = { "int" : "intégrale", "sqrt" : "racine carrée", "frac" : "fraction"}

for i in D.keys():
    print(i)

int
sqrt
frac

for i in D:
    print(i)

int
sqrt
frac

for i in D.items():
    print(i)

('int', 'intégrale')
('sqrt', 'racine carrée')
('frac', 'fraction')

for i in D.keys():
    print(D[i])

intégrale
racine carrée
fraction

Fonctions

def f(x):
    return 2*x

f(7)

14

def f(x):
    print(2*x)

f(7)

14

def somme(x,y):
    z=x+y
    return z

somme(2,4)

6

def f(n):
    x=1
    for i in range(n):
        x=x*(i+1)
    return x

f(5)

120

Portée lexicale

lorsqu’une expression fait référence à une variable à l’intérieur d’une fonction, Python cherche la valeur définie à l’intérieur de la fonction et à défaut la valeur dans l’espace global du module.

https://pythontutor.com/

def f():
    x=2
    y=x+2
    print(y)    

x=5
f()
print(x)

4
5

def f():
    y=x+2
    print(y)

x=5
f()
print(x)

7
5

def f():
    x=x+2
    print(x)

x=5
f()
print(x)

---------------------------------------------------------------------------
UnboundLocalError                         Traceback (most recent call last)
<ipython-input-66-f2b4749272e2> in <module>
      1 x=5
----> 2 f()
      3 print(x)

<ipython-input-65-9f8b1a4cacb7> in f()
      1 def f():
----> 2     x=x+2
      3     print(x)

UnboundLocalError: local variable 'x' referenced before assignment

def f(x):
    x=x+2

x=2
f(x)
print(x)

2

def f(L):
    L[0] =L[0]+2

L=[2]
f(L)
print(L)

[4]

Divers

Commentaires

# fonction factorielle

def f(n):
    """calcule le factoriel de l'entier n"""
    x=1
    for i in range(n):
        x=x*(i+1)
    return x

help(f)

Help on function f in module __main__:

f(n)
    calcule le factoriel de l'entier n

assert

aide à la recherche d'erreur

def f(n):
    x=1
    for i in range(n):
        x=x*(i+1)
    return x

f(1.5)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-74-8f62b0ae53ed> in <module>
----> 1 f(1.5)

<ipython-input-73-3d98c8bf9be3> in f(n)
      1 def f(n):
      2     x=1
----> 3     for i in range(n):
      4         x=x*(i+1)
      5     return x

TypeError: 'float' object cannot be interpreted as an integer

def f(n):
    assert n==int(n) and n>=0
    x=1
    for i in range(n):
        x=x*(i+1)
    return x

f(5)

120

f(-5)

---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-77-8afe41f7933d> in <module>
----> 1 f(-5)

<ipython-input-75-c3c670256434> in f(n)
      1 def f(n):
----> 2     assert n==int(n) and n>=0
      3     x=1
      4     for i in range(n):
      5         x=x*(i+1)

AssertionError: 

f(1.5)

---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-78-8f62b0ae53ed> in <module>
----> 1 f(1.5)

<ipython-input-75-c3c670256434> in f(n)
      1 def f(n):
----> 2     assert n==int(n) and n>=0
      3     x=1
      4     for i in range(n):
      5         x=x*(i+1)

AssertionError: 

Importation de modules

import numpy
print(numpy.pi, numpy.cos(numpy.pi))

3.141592653589793 -1.0

import numpy as np
print(np.pi, np.cos(np.pi))

3.141592653589793 -1.0

from numpy import pi, cos
print(pi, cos(pi))

3.141592653589793 -1.0

à éviter :

from numpy import *
from math import *
print(pi, cos(pi))

3.141592653589793 -1.0