Python Keywords and allowed Variable names

3. Python Keywords and allowed Variable names#

# To retrieve the python keyword list, we can use the keyword built-in package.
import keyword

Let’s print the keywords present.

keyword.kwlist returns python’s keywords in a list datatype.

We are using *(starred) expression to print the values returned by keyword.kwlist each separated by “\n”(newline).

print(*keyword.kwlist, sep="\n")

False
None
True
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3.1. Variable Names#

TLDR:

  • Variable names shouldn’t be same as that of built-in keywords.

  • Variable name shouldn’t start with a number or with a symbol(except “_”, protected and private attributes are created using underscore, 🤔 it’s better to say it as name mangling rather than protected or private. That’s for a different notebook session 😀).

PS: Don’t give a try naming the variable that starts with #, it would be a Python’s comment, which would be neglected by the interpreter 😅.

3.1.1. Allowed Variable names#

x = True
_x = False
x_y = "Hey Python geek!"
x9 = "alphabet_number"
# Python is a case sensitive language, so `x` is different from `X`. Let's give it a try.
X = "one more variable"
print(f"x is equal to X:{x==X}")

x is equal to X:False

3.1.2. Invalid Variable names#

We will be using exec within try-except to catch the syntax error. 🤔 But why? Syntax errors can’t be caught, well it shouldn’t for good 😉. so we are using exec to execute the code.

exec takes the string argument and interprets the string as a python code.

# variable name starting with number.
code_string = "9x=True"
try:
    exec(code_string)
except SyntaxError as exc:
    print(f"Ouch! In the exception: {exc}")

Ouch! In the exception: invalid decimal literal (<string>, line 1)

# variable name starting with a symbol(other than underscore"_").
code_string = "$g = 10"
try:
    exec(code_string)
except SyntaxError as exc:
    print(f"Ouch! In the exception: {exc}")

Ouch! In the exception: invalid syntax (<string>, line 1)
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