Step 3 - Elif

In the previous example, we checked the source language code and not the target language code. In this step, we will introduce an and statement and also the elif statement.

The and statement is a logical operator that combines the check for both source language and target language. The elif statement allows us to introduce multiple different logical checks.

  • Create a new file called lab_7_step_3_elif.py and add the following code:
import json

# A defined list of languages supported by Amazon Translate
languages = ["af","sq","am","ar","az","bn","bs","bg","zh","zh-TW","hr","cs","da","fa-AF","nl","en","et","fi","fr","fr-CA","ka","de","el","ha","he","hi","hu","id","it","ja","ko","lv","ms","no","fa","ps","pl","pt","ro","ru","sr","sk","sl","so","es","sw","sv","tl","ta","th","tr","uk","ur","vi"]

# This uses a json string as an input
json_string = """
{
    "Input":[
        {
        "Text":"I am learning to code in AWS",
        "SourceLanguageCode":"en",
        "TargetLanguageCode":"fr"
        }
    ]
}
"""

json_input = json.loads(json_string)

SourceLanguageCode = json_input['Input'][0]['SourceLanguageCode']
TargetLanguageCode = json_input['Input'][0]['TargetLanguageCode']

# Uses an if-elif-else statements to check that the SourceLanguageCode is in the languages list.
if SourceLanguageCode == TargetLanguageCode:
    print("The SourceLanguageCode is the same as the TargetLanguageCode - nothing to do")
elif SourceLanguageCode not in languages and TargetLanguageCode not in languages:
    print("Neither the SourceLanguageCode and TargetLanguageCode are valid - stopping")
elif SourceLanguageCode not in languages:
    print("The SourceLanguageCode is not valid - stopping")
elif TargetLanguageCode not in languages:
    print("The TargetLanguageCode is not valid - stopping")
elif SourceLanguageCode in languages and TargetLanguageCode in languages:
    print("The SourceLanaguageCode and TargetLanguageCode are valid - proceeding")
else:
    print("There is an issue")

  • To run the program, enter the following command in the terminal:

    python lab_7_step_3_elif.py

Test

Test the code by changing the values of the SourceLanguageCode and the TargetLanguageCode.

  1. Make the SourceLanguageCode and TargetLanguageCode identical values.
  2. Change the SourceLanguageCode and TargetLanguageCode to different but not valid values.
  3. Change the SourceLanguageCode to a value not supported and TargetLanguageCode to a supported value.
  4. Change the SourceLanguageCode to a supported value and the TargetLanguageCode to a not supported value.
  5. Change both the SourceLanguageCode and TargetLanguageCode to supported but different values.

What did we do?

  • We use our original if statement to check if the source and target languages are equivalent
  • We used an and logical operator to check both the SourceLanguageCode and TargetLanguageCode are valid.
  • We then used elif a not in combined with the and logical operators to check if neither of the SourceLanguageCode or TargetLanguageCode are valid.
  • We then used two elif statements to determine if either the SourceLanguageCode or TargetLanguageCode are valid.
  • Finally we used an else statement to catch any other condition.

What did python do?

  • Python checked each of the statements, to see if they returned a True or False. If it returned False, it continues to the next statements in turn to check if they are True or False until it reaches a True statement or else. If it finds a matching statement, it runs the code corresponding to the elif and then skips the rest.