Note Avant toute chose, veuillez choisir votre langue dans le menu Langs (attention à ne pas avoir les 2 langues en même temps).

Note First of all, please choose your language from the Langs menu (be careful not to have both languages at the same time).

Python as a calculator¶

The Python programming language can be used interactively to know that when you type a command, Python executes it immediately and displays the answer:

In [1]:
1+1
Out[1]:
2

Notes on the environment Jupyter¶

  • A cell can have 3 states:
    • not selected (no frame around the cell) * selected (blue frame)
    • selected and in edit mode (green frame)
  • Click to select a cell (or sometimes passes it directly into edit mode for calculation cells)
  • Double click selects and goes into edit mode (on a text box, the Markdown syntax appears)
  • Enter like clicking allows to go down in the states when Esc allows to go up
  • To have Python recalculate the result of a cell, do Shift + Enter (display the pretty display for text cells)

Exercise: modify the calculation cell above to calculate 1 + 2

In [2]:
print(1 + 7*2)
print(49**0.5)
print(7 % 5)

15
7.0
2

The print command allows to display a result which is different from the result of the cell (which is the result of the last command).

Python has basic operators (including the ** operators for power and % for the modulo). For more advanced mathematical functions we must import libraries (we will see later what libraries are). We start with the scientific library NumPy:

In [3]:
from numpy import * 
print(sin(3.14))
print(sin(pi))
print(log(e))

0.0015926529164868282
1.2246467991473532e-16
1.0
In [4]:
log2(16)
Out[4]:
4.0

For documentation on a function use ? (Specific to iPython). In regular Python we do help (log). You have to run the cell (Shift + Enter) to see the result in a pane at the bottom of the page (click on the cross to close it or type Esc on a cell in edit mode).

In [5]:
?log

Complexes¶

Complexes exist but the imaginary number is j and you have to write 1j and not just j:

In [6]:
1j**2
Out[6]:
(-1+0j)
In [7]:
sqrt(1j)
Out[7]:
(0.7071067811865476+0.7071067811865476j)
In [8]:
e**(pi*1j)
Out[8]:
(-1+1.2246467991473532e-16j)

Note the rounding error in the $e^{i \pi}$ calculation for the imaginary part.

The order of priority of the operators¶

The order of priority of the operators is:

  1. ** the power
  2. -x, + x the unit operator minus or plus
  3. *, /, // (// being the entire division)
  4. % the modulo
  5. +, -
In [9]:
print( -3**2 )
print( 9/3*3 )
print( 9/(3*3) )

-9
9.0
1.0

Errors¶

Finally, we check the error messages to correct the code:

{{ PreviousNext("../lesson0 Introduction/Introduction.ipynb", "01 - Les variables.ipynb") }}

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