The Python interpreter has a number of functions and types
built into it that are always available. They are listed here in alphabetical order.
You don't need to import them, they are already available in your global scope.
We are going to review 6 built-in functions (more if we have time):
1. len
2. input
3. print
4. open
5. range
6. typelen is another built-in function, it returns the number of element into something
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my_name = "Christian"
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# 9 letters
len(my_name)
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my_list = [1,2,3,4,5]
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# elements inside a list
len(my_list)
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# elements inside a dictionary
my_dict = {"first": "1", "second": "2"}
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len(my_dict)
Out[61]:
Input reads a value from you terminal and saves it inside the variable
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my_input = input('type your variable: ')
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my_input
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Literally it puts somthing in your stdout, and in general it means your terminal/console.
Together with print we introduce a way to format strings.
Let's say that I want to print:
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# This is a `way`
print("My name is Christian and I am 29 years old")
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# This is another way
my_first_name = "Christian"
my_age = 29
print("My name is", my_first_name, "and I am", my_age, "years old")
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# This is the proper way
print(f"My name is {my_first_name} and I am {my_age} years old")
How does it work?
We use f"" notation (can be also f'') and put our variables inside curly brackets.
It works also when you want to create new strings.
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sentence = f"My name is {my_first_name} and I am {my_age} years old"
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print(sentence)
Open is used when you want to read/write files
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my_file = open("text.txt", mode='w+')
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# returns the number of characters written
my_file.write("This is my first file\n")
Out[4]:
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my_file.write("This is the second line\n")
Out[5]:
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# this is very important!
my_file.close()
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# We didn't cover context manager,
# but this is the Pythonic way to work with files
with open("text.txt", mode='w+') as my_file:
my_file.write("This is my first file\n")
my_file.write("This is the second line\n")
How want to create a list with the numbers for 0 to 10, with 10 not inclued
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my_list = []
number = 0
while number < 10:
my_list.append(number)
number += 1
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my_list
Out[4]:
Can we do this in 1 line?
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my_list = list(range(10))
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my_list
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Range is actually an immutable sequence type and the sequence can be created in this way:
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# Remember `stop` is not included
list(range(1,6))
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# You can use step to `jump` between the numbers
list(range(0,11,2))
Out[11]:
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# Remember that range is not a list!
range(10)
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Type is our last built-in function for this part, it returns the type of our variable (object)
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my_name = "Christian"
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type(my_name)
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my_list = [1,2,3,4,5]
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type(my_list)
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my_dict = {"first": "1", "second": "2"}
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type(my_dict)
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type(my_dict) is type(my_list)
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type(my_list) is type(my_list)
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This is very useful when you want to check if 2 variables have the same type, thus the could behave in the same way....
keypoints:
for loop must end with a colon, and the body must be indented."for loop is made up of a collection, a loop variable, and a body."range to iterate over a sequence of numbers."The short answer is always use built-in functions, generally they are:
* faster
* well tested
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%%timeit
my_list = []
number = 0
add_to = my_list.append
while number < 1000:
add_to(number)
number += 1
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%%timeit
my_list = list(range(1000))
my implementation is ~5 times slower.
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my_list = list(range(10000))
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%%timeit
number = 0
for element in my_list:
number += 1
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%%timeit
len(my_list)
# Challenge n.1
print("Print the even numbers between 0 and 20 (20 included)")
for ______ in ______:
if ______ % 2 == 0:
print(______)
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# Put your code here
# Challenge n.2
print("Save the even numbers between 0 and 20 (20 included)")
for ______ in ______:
if ______ % 2 == 0:
with open("my_file.txt", mode="w") as f:
f.write(______)
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# Put your code here
# Challenge n.3
print("Save a list of 100 numbers in a files and then read them and print the odd numbers")
with open("my_file.txt", mode="w") as f:
for ______ in range(100):
f.write(______)
______ ______ as ______:
for ______ in f:
if ______ % 2 != 0:
print(______)
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# Put your code here
# Challenge n.4
# Check if the num and name are of the same type
num = 10
name = "Christian"
if ______ is ______:
print("Our variables are of the same type")
else:
print("Our variables are of a different type")