Day 4 - Iteration & Loops

Author: codingforentrepreneurs

tutorial-reference/Day 4/Day 4 - Iteration & Loops.md

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+# Day 4 - Iteration & Loops
+
+
+
+### The `for` loop:
+```
+🕹 % python3
+Python 3.8.2 (v3.8.2:7b3ab5921f, Feb 24 2020, 17:52:18) 
+[Clang 6.0 (clang-600.0.57)] on darwin
+Type "help", "copyright", "credits" or "license" for more information.
+>>> my_list = [1,2,3,4,5]
+>>> my_list[0]
+1
+>>> my_list[1]
+2
+>>> my_list[2]
+3
+>>> my_list[3]
+4
+>>> my_list[4]
+5
+>>> for my_var in my_list:
+... print(my_var)
+... 
+1
+2
+3
+4
+5
+>>> my_var
+5
+>>> for i in "abc":
+... print(i)
+ File "<stdin>", line 2
+ print(i)
+ ^
+IndentationError: expected an indented block
+>>> 
+>>> for i in "abc":
+... print(i)
+... print(i)
+ File "<stdin>", line 3
+ print(i)
+ ^
+IndentationError: unindent does not match any outer indentation level
+>>> for i in "abc":
+... print(i)
+... print(i)
+... 
+a
+a
+b
+b
+c
+c
+>>> "abc"[1]
+'b'
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> 
+>>> for x in 10:
+... print(x)
+... 
+Traceback (most recent call last):
+ File "<stdin>", line 1, in <module>
+TypeError: 'int' object is not iterable
+>>> for x in "10":
+... print(x)
+... 
+1
+0
+>>> for x in range(0, 10):
+... print(x)
+... 
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+>>> user_1 = {'username': 'jmitchel3', 'id': 1}
+>>> user_2 = {'username': 'abc', 'id': 2}
+>>> my_users = [user_1, user_2]
+>>> for user in my_users:
+... print(user)
+... 
+{'username': 'jmitchel3', 'id': 1}
+{'username': 'abc', 'id': 2}
+>>> for user in my_users:
+... print(user['username'])
+... 
+jmitchel3
+abc
+>>> for user in my_users:
+... print(user['email'])
+... 
+Traceback (most recent call last):
+ File "<stdin>", line 2, in <module>
+KeyError: 'email'
+>>> user_2 = {'username': 'abc', 'id': 2, 'email': 'abc@abc.abc'}
+>>> print(my_users)
+[{'username': 'jmitchel3', 'id': 1}, {'username': 'abc', 'id': 2}]
+>>> my_users = [user_1, user_2]
+>>> print(my_users)
+[{'username': 'jmitchel3', 'id': 1}, {'username': 'abc', 'id': 2, 'email': 'abc@abc.abc'}]
+>>> for user in my_users:
+... print(user['email'])
+... 
+Traceback (most recent call last):
+ File "<stdin>", line 2, in <module>
+KeyError: 'email'
+>>> for user in my_users:
+... if 'email' in user:
+... print(user['email'])
+... 
+abc@abc.abc
+>>> selected_user = {}
+>>> my_user_lookup = 2
+>>> for user in my_users:
+... if 'id' in user:
+... if user['id'] == my_user_lookup:
+... selected_user = user
+... 
+>>> print(selected_user)
+{'username': 'abc', 'id': 2, 'email': 'abc@abc.abc'}
+>>> for x in range(0, 10):
+... print(x)
+... 
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+>>> for x in range(0, 10):
+... for user in my_users:
+... if user['id'] == x:
+... print(user)
+... 
+{'username': 'jmitchel3', 'id': 1}
+{'username': 'abc', 'id': 2, 'email': 'abc@abc.abc'}
+```