[Python] Basic pattern and usage of if statement (comparison operator and Boolean operator)

[Python] Basic pattern and usage of if statement (comparison operator and Boolean operator)

A review of the if statement pattern.

1. [Basic syntax of if statement](# 1 Basic syntax of if statement)
2. [No conditional branch](#No conditional branch)
3. [Conditional branching (else only)](#Conditional branching else only)
4. [Two or more conditional branches (without else)](#Two or more conditional branches without else)
5. [Two or more conditional branches (with else)](# Two or more conditional branches with else)
6. [Conditional expression operator](# 2 Conditional expression operator)
7. [Operator list](# 3 Operator list)
8. [Example of comparison operator](# 4 Example of comparison operator)
9. ["==" equal](# equal)
10. ["! =" Not equal](# Not equal)
11. [Greater than ">" (not included)](greater than # not included)
12. ["> =" or more (including)](# or more included)
13. [Less than "<" (not included)](not including #)
14. ["<=" Or less (including)](# including below)
15. [Includes "in" element](includes # element)
16. [Do not include "not in" element](Do not include # not-in element)
17. [Equal "is" objects](#Equal objects)
18. [Example of Boolean operator](# 5 Example of Boolean operator)
19. ["and" and](# and)
20. ["or" or](# or)
21. [Not "not"](not #)

① No conditional branch ② One conditional branch. True or False ③ Two or more conditional branches. Processing is executed only under the specified conditions. ④ Two or more conditional branches. Also set the processing in case of false

▼ ① No conditional branch

If the conditions are not met, do nothing.

Pattern 1 (no conditional branching)

if A:
    AAA

"A": Conditional expression "AAA": Processing when A holds

• Add ":" to the end of the conditional expression.
• The pattern executed in the if statement lowers the indent. (In the case of a general editor, if you add a ":" and start a new line, the indent will be added automatically)

Example (no conditional branch, True)

A = 100

if A == 100:
    print('A is 100.')

#output
#A is 100.

Example (no conditional branch, False)

A = 90

if A == 100:
    print('A is 100.')

Pattern 2 (else)

if A:
    AAA
else:
    BBB

"A": Conditional expression "AAA": Processing when A holds "Else:": When A does not hold "BBB": Processing when A does not hold

• No conditional expression is required after else.
• "Else:" is always ** set with a double colon **.

Example (with conditional branching, else)

A = 90

if A == 100:
    print('A is 100.')
else:
    print('A is not 100.')

#output
#A is not 100.

Pattern 3 (elif)

if A:
    AAA
elif B:
    BBB
elif C:
    CCC

"A": Conditional expression "AAA": Processing when A holds "Eli if B": Second conditional expression "BBB": Processing when B holds "El if C": Third conditional expression "CCC": Processing when C holds

• Multiple "elif" can be set. (Only 2 in the above)
• "Elif conditional expression:" Add ":" at the end of the conditional expression
• Check the conditions from above, and the process ends when it becomes True.
• If the conditions of "if" and "elif" are not met, no processing is performed.

Example (with conditional branching, elif, True)

A = 70

if A == 100:
    print('A is 100.')
    
elif A == 80:
    print('A is 80.')
    
elif A == 70:
    print('A is 70.')

#output
#A is 70.

Example (multiple matching conditions)

A = 70
B = 100

if A == 100:
    print('A is 100.')
    
elif B == 100:
    print('B is 100.')
    
elif A == 70:
    print('A is 70.')

#output
#B is 100.

It ends when the conditions are met from the top. └ Both "B == 100" and "A == 70" are True, but the process ends when the above "B == 100" becomes True.

Pattern 3 (elif, else)

if A:
    AAA
elif B:
    BBB
elif C:
    CCC
else:
    DDD

"A": Conditional expression "AAA": Processing when A holds "Eli if B": Second conditional expression "BBB": Processing when B holds "El if C": Third conditional expression "CCC": Processing when C holds "Else:": If none of the conditions are met "DDD": Processing when none of the conditions are met

• Multiple "elif" can be set. (Only 2 in the above)
• "Elif conditional expression:" Add ":" at the end of the conditional expression

Examples (elif, else)

A = 50

if A == 100:
    print('A is 100.')
    
elif A >= 80:
    print('A is over 80.')
    
elif A >= 70:
    print('A is over 70.')
    
else:
    print('A is 70 or less.')

#output
#A is 70 or less.

** ▼ There are two types of operators ** -Comparison of "comparison operator" elements -A combination of "Boolean operators" conditional expressions

3. 3. Operator list

① "==" equal

There are two equals. An error will occur if there are one or three or more.

(One equal is an assignment to a variable)

「=="equal

A = 100

if A == 100:
    print('A is 100.')
else:
    print('A is other than 100.')

#output
#A is 100.

When "!" Is added at the beginning, it means "not".

「!=Not equal

A = 100

if A != 100:
   print('A is other than 100.') 
else:
   print('A is 100.')

#output
#A is 100.

Supplement: The name of "!" Exclamation mark, exclamation mark, surprise mark

③ Larger than ">"

A = 50

if A > 50:
   print('A is greater than 50.') 
else:
   print('A is 50 or less.')

#output
#A is 50 or less.

「＞="that's all(Including)

A = 50

if A >= 50:
   print('A is greater than 50.') 
else:
   print('A is 50 or less.')

#output
#A is greater than 50.

Less than "<" (not included)

A = 50

if A < 50:
   print('A is less than 50.') 
else:
   print('A is 50 or more.')

#output
#A is 50 or more.

「＜=Below (including)

A = 50

if A <= 50:
   print('A is 50 or less.') 
else:
   print('A is greater than 50.')

#output
#A is 50 or less.

⑦ Including "in" element

if A in B └ A is included in B.

• A is shorter. B is longer.

Includes "in" element

A = 'pen'
B = 'I have a pen'

if A in B:
   print('Yes') 
else:
   print('No')

#output
# Yes

Does not include "not in" element

A = 'I have a pen'
B = 'pen'

if B not in A:
   print('Yes') 
else:
   print('No')

#output
# No

Stricter than "==".

"Is" objects are equal

A = 'I have a pen'
B = 'I have a pen'

if A is A:
   print('Yes') 
else:
   print('No')

#output
# Yes

"Is" Comparison of different objects

A = 'I have a pen'
B = 'I have a pen'

if A is B:
   print('Yes') 
else:
   print('No')

#output
# No

① "and"

if A and B: └ "A" "B" conditional expression

• Any number of conditions can be combined.

"And"

a = 1
b = 2

if a == 1 and b == 2:
    print('a=1, b=2')
else:
    print('a=1, b=Not 2')

#output
# a=1, b=2

"And" and example 2

a = 1
b = 2
c = 3

if a == 1 and b == 2 and c != 3:
    print('a=1 and b=2 and 3 is other than 3')
else:
    print('a=1 and b=2 and 3 is not other than 3')

#output
# a=1 and b=2 and 3 is not other than 3

"And"

a = 1
b = 2
c = 3

if a == 1 and b == 2 or c != 3:
    print('a=1 and b=2 or 3 is other than 3')
else:
    print('a=1 and b=2 or 3 is not other than 3')

#output
# a=1 and b=2 or 3 is other than 3

"And" and "or"

a = 1
b = 2
c = 3

if a == 100 and b == 200 or c != 3:
    print('a=1 and b=2 or 3 is other than 3')
else:
    print('a=1 and b=2 or 3 is not other than 3')

#output
# a=1 and b=2 or 3 is not other than 3

③ Not "not"

if not A: └ Add to the beginning of the conditional expression

Not "not"

a = 100
b = 100

if not a == b:
    print('a=not b')
else:
    print('a=b')

#output
# a=b

「!=Will be the same as

a = 100
b = 100

if a != b:
    print('a=not b')
else:
    print('a=b')

#output
# a=b

＞ For statement here