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Keywords in Python and C

Ashok Be
hackgenius
Published in
7 min readSep 3, 2018

How to start comparing two programming languages? Begin at the core by analyzing the keywords (a small set of words that are important to the language, and reserved) that are exclusive to both languages.

UPDATE Mar 2024: Added lambda to the unique keyword list in Python.

Comparing Python and C through Keywords

As reported elsewhere (http://j.mp/reservedWords), here are some popular languages and the count of keywords in each of them.

For quite some time, with only 31 keywords, Python (Version 2) had held the distinction of being the “language with the least number of keywords”. Of course, we need to ignore Smalltalk (6) and the not-yet-mainstream Go (25) and Elm (25).

But with the transition to Python 3, that distinction has been ceded back to the good old C language (total keywords is 32). In any case, I was quite curious as to what were the additional keywords that were added to the language. Here’s what I came up with:

  • In the transition from Python_2 to Python_3, there have been six changes to the keyword list — four were added and two were removed, resulting in a net addition of two.
  • UPDATE (May 2023): Python 3.9.5 now has 36. Launch this!
Python 3.9.5 keywords has one extra.

Net Change is +6–4 = +2

Keywords added to Python_3: {'None', 'nonlocal',  'True', 'False'}
Keywords removed from: {'print', 'exec'}
Total changes: 6

Note: Both print and exec have been removed as keywords but retained as built-in functions. For an in-depth and insightful answer on behaviour of exec in Python 3 vis-à-vis Python 2, read this.

“Core” Python versus “Core” C

If you really think about it, it is not an apples-to-apples comparison when you compare the count of keywords in a strictly typed language (C, Java, etc.) versus a dynamic language (Python). Also, C does not have syntax that supports object-oriented programming or exception handling, whereas Python does.

Nevertheless, for the benefit of a developer/student who is familiar with core Python and is keen on familiarizing with the core part of the C language, the journey can start with a critical inspection of the keywords in both the languages. While “type-less” C has 21 keywords, “essential” Python (sans keywords related to objected orientation and exception handling) has 16 keywords.

-----------------------
Comparing keywords in Python and type-less C
-----------------------
Python: ['break', 'class', 'continue', 'def', 'del', 
'else', 'for', 'global', 'if', 'in', 'is', 
'nonlocal', 'pass', 'return', 'while'] 
# Total - 15 "type-less" C Language: ['auto', 'break', 'const', 
'continue', 'do', 'else', 'enum', 'extern', 'for', 
'goto', 'if', 'lambda', 'register', 'return', 'sizeof', 
'static', 'struct', 'typedef', 'union', 'void', 
'volatile', 'while'] 
# Total - 21

If you remove the keywords that are common to both the above lists, here’s what remains:

------ DIFFERENCE -------
extra in python: ['class', 'def', 'del', 
'global', 'in', 'is', 'lambda', 'nonlocal', 'pass'] 9extra in clang: ['auto', 'const', 'do', 'enum', 
'extern', 'goto', 'register', 'sizeof', 'static', 
'struct', 'typedef', 'union', 'volatile'] 14

My analysis below will attempt to compare and contrast the two languages by referring to the above 22 keywords (8 that exists only in Python verus 14 that exists only in C language).

Part 0 (programming constructs)

  • The do-while loop construct exists in C, but not in Python.
The difference can be almost life and death!
  • enum exist in C to give variable-like labels to numeric values. You can also define constant values (and macros) using preprocessor directives (#define). There is no support for something like this in Python.
  • C has the keywordsswitch-case-default that help implement the multi-conditional constructs which can be quite elegant when used with enum. The equivalent of this can be codified with a series of non-elegant if-elif statements or using the more elegant dict datatype in Python.
  • goto allows you to jump to an arbitrary location in the Ccode, and allowing for obscure source code to be written. And for that reason, it is recommended that this keyword be used sparingly. But then, see below for a code snippet from the Linux kernel code that uses goto. Go figure. There is no support for this kind of conditional jumps in Python.
code snippet from the Linux kernel that uses goto
  • A function or class definition in Python requires def which is not required in C. lambdais a keyword used to create anonymous functions in Python.
  • pass - a Python statement which has no effect; the equivalent of this is best achieved in C by using the ; delimiter.

Part 1 (scope)

  • Scope options are accomplished by using global and nonlocal in Python, whereas in C the keywords auto, static and extern are used.
  • C continues to be one of the few languages that allows you to get close to the metal, and that is why it has keywords like register and volatile.
  • For example, keyword volatile is used to declare volatile variables, which are variables that can be changed by external factors, such as hardware devices.
  • The keyword register is used to declare register variables, which are variables that are stored in CPU registers instead of memory. “A CPU register can be accessed in less than a CPU cycle on modern super-scalar CPUs (as opposed to going to memory which can take 100–300 CPU cycles.”

Part 2 (objects and immutability)

  • Python supports object-oriented programming with the class keyword whereas the closest equivalents in C would be struct and typedef. The memory-efficient construct union, is unique to C and is not found in other strictly typed languages.
  • In Python, where everything is an object, there is an explicit del keyword.
  • At compile time, the C programmer can signal the need for immutability by using const as a prefix along with the data type. In Python, the mutability or immutability of an object is determined by its type.

Part 3 (object inspection)

  • Member introspection in a sequence or collection is possible in Python using the inkeyword - there is no equivalent of that in C.
  • Object equivalence is supported in Python and the keyword is is used to accomplish this. It returns False even if the objects are 100% equal.
Object equivalence checking in Python.

Part 4 (related to memory)

  • sizeof- is it a macro or a keyword? that’s a source for intense debate. The keyword is typically used when invoking dynamic memory allocation. In contrast, explicit memory management is non-existent in Python.
  • A comparison of the operators supported in the languages highlights a significant difference: C language heavily utilizes pointers. Using the unary & and * (address and de-referencing) operators, pointer variables in C allows the programmer to “write to the metal”, i.e. have direct access to and modification of memory.

Misc

Remember, the above analysis has been about comparing “type-less” C and “non-OOP and exception handling free” Python. Again, an important capability of the C language is its support for preprocessor directives (using #define and #undef) for defining macros.

For contrast, also see the typical (and rather boring!) analysis of these two languages at https://medium.com/edureka/python-vs-c-b83446bc2c23 .

Pop Quiz

What does Python dynamically provide for that the C language doesn’t? What does the C language dynamically provide for that Python doesn’t?

Program listing

The above lists of keywords were generated using a Python (Version 3) program which is listed below.

import keyword
python3 = keyword.kwlist# this can be obtained from a Python2 interpreter
# by using the above two statements 
#
python2 = [
	'and', 'as', 'assert', 'break', 'class', 'continue',
	'def', 'del', 'elif', 'else', 'except', 'exec', 
	'finally', 'for', 'from', 'global', 'if', 'import', 
	'in', 'is', 'lambda', 'not', 'or', 'pass', 'print',
	'raise', 'return', 'try', 'while', 'with', 'yield'
]# new keywords in Python 3 
additional = set(python3) - set(python2)
print("Keywords added to Python3:", additional)removed = set(python2) - set(python3)
print("Keywords removed from:", removed)print("Total changes:", len(additional) + len(removed))
print("-----------------------")
print("Comparing keywords in Python and C")
print("-----------------------")'''
# get keywords for C from webpages 
# write a scrap program by processing links in   
  https://www.programiz.com/c-programming/list-all-keywords-c-language
  
  http://tigcc.ticalc.org/doc/keywords.html#switch
'''
clang = []
with open("programiz.txt", "r") as fp:
  links = fp.readlines()
  for link in links: 
    try:
      link.index("list-all-keywords-c-language#") 
      hashsymbol = link.find("#")
      keyword = link[hashsymbol+1:-1]
      #print("found keyword", keyword)
              list = keyword.split("_")      clang.extend(klist)
    except:
      passclang.extend(["size_t", "NULL"])clangRemove = [
    'NULL',
    'char', 'int', 'float', 'double', 'long', 'size_t', 'void',
    'short', 'unsigned', 'signed',
    'switch', 'case', 'default',
    # 'auto', 'volatile', 'register', 
    # 'enum', 'typedef',
]clang = [
    keyword for keyword in clang 
    if keyword not in clangRemove
]pythonRemove = [
    'None', 'False', 'True',
    'assert', 'with', 'yield', 'lambda',
    'try', 'except', 'finally', 'raise',
    'import', 'from', 'as', 
    'and', 'or', 'not',
    'elif'
]python3 = [
    keyword for keyword in python3
        if keyword not in pythonRemove
]print("Python:", sorted(python3), len(python3))
print()
print("'typefree' C Language:", sorted(clang), len(clang))
print("\n------ DIFFERENCE -------")
pextra = set(python3) - set(clang)
cextra = set(clang) - set(python3)
print("extra in python:", sorted(pextra), len(pextra))
print("extra in clang:", sorted(cextra), len(cextra))

Program Output

Keywords added to Python3: {'None', 'nonlocal', 
'True', 'False'}
Keywords removed from: {'print', 'exec'}
Total changes: 6
-----------------------
Comparing keywords in Python and C
-----------------------
Python: ['break', 'class', 'continue', 'def', 'del', 
'else', 'for', 'global', 'if', 'in', 'is', 
'nonlocal', 'pass', 'return', 'while'] 15'typefree' C Language: ['auto', 'break', 'const', 
'continue', 'do', 'else', 'enum', 'extern', 'for', 
'goto', 'if', 'register', 'return', 'sizeof', 
'static', 'struct', 'typedef', 'union', 'void', 
'volatile', 'while'] 21------ DIFFERENCE -------
extra in python: ['class', 'def', 'del', 'global', 
'in', 'is', 'nonlocal', 'pass'] 8
extra in clang: ['auto', 'const', 'do', 'enum', 
'extern', 'goto', 'register', 'sizeof', 'static', 
'struct', 'typedef', 'union', 'volatile'] 14

Useful links

Programming
Python
Keywords
Insights
C Language

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Ashok Be
hackgenius

Written by Ashok Be

321 Followers
Editor for

Entrepreneur, struggle-to-code evangelist, paradox collector, green tea and black coffee enthusiast. And yes, squash!

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